StudyGuide Adv electronics
Contents
1. Study Guide When referring to the two ends of a diode we use the ee terms Anode for the P material end and Cathode for the N material end A silicon diode will begin to conduct when the anode end is approximately 5 to 7 volts higher than the cathode end In the illustration of the diode symbol shown notice the arrow on the anode end The arrow shows the current flow direction when viewed in a conventional plus to minus manner Also notice there is a stripe on the outside of a diode The stripe is used to Alone signify the cathode end of the device Diode with schematic symbol Forward Bias Diodes can be inserted into a circuit in either a Forward Bias or Reverse Bias configuration In a forward biased application the anode is connected to the more positive part of a circuit while the cathode is connected to a more negative part of the circuit When power is applied to a silicon diode and the barrier voltage exceeds 5 to 7 volts current is allowed to flow through the diode and therefore through the circuit Notice in this circuit that the diode does not conduct until the applied voltage matches the rated barrier voltage of the device The diode behaves like an open in a circuit and drops all of the applied voltage until the barrier voltage is reached Once the applied voltage exceeds the barrier voltage the voltage drop across the diode will remain the same regardless of addition2. ay a nh e ek n n a di dp ai ae jp AC Refrigerant TF Sensor i Pressure Sensor Sensor Ground l Signal Signal L T Typical Input Sensor Schematic Voltage Generators In addition to variable resistor sensors there are a number of input sensors that actually produce their own voltage known as Voltage Generators Voltage generators can be electromagnetic chemical or Photovoltaic Electro Magnetic Sensors Electro Magnetic sensors are made of a coil of wire wound around a permanent magnet and use a metal sensor ring that turns very close to the sensor As the sensor ring begins to rotate the magnetic field is disrupted and an AC voltage is produced The frequency of this sensor output is then translated into a rotational speed value the computer can use Some examples of Electro Magnetic sensors include Anti Lock Wheel Speed Sensors WSS Crankshaft Position Sensors CKP Distributor Pick Up Camshaft Sensors CMP Vehicle Speed Sensors VSS Input Speed Sensors ISS Output Speed Sensors OSS Wheel Speed Sensor Electro Magnetic Sensor 203 2004 2006 Melior Inc Advanced Electronics Study Guide Chemical Voltage Generator The most commonly used chemical voltage generator is the Oxygen Sensor O2 This sensor produces an output from 0 Volts to approximately 1 Volt when the oxygen in the exhaust stream reacts with the platinum coating o
3. where the switch would indicate the opening and closing of a door 10 22004 2006 Melior Inc Exercise Blower Motor Circuit 1 In the circuit shown here 2 What is the total what is the total resistance of above resistance with the circuit with blower switch blower switch in LOW set to MED position position Bu Bu 1 80 1 80 JA 2580 Bom 3 The total resistance of 4 With the blower in HI circuit equals how many position how many amps Ohms with blower in HI will this circuit draw position SL 10 amps 1 80 20 amps 442 00 25 amps Au 230 amps 5 How many amps will the How many amps will the blower circuit draw in blower circuit draw in LOW position MED position 2 0 amps 2 0 amps 4 2 amps 4 2 amps 28 6 amps amps 115 amps 115 amps What is the minumum d Haw much voltage is fuse that should be used dropped at R 1 with in this circuit blower switch in LOW position 5 amps volts 10 amps 4 2 volts _ 15 amps _ 6 3 volts _ 30 amps 12 volts 11 How many volts are 12 The total power dropped at the blower consumed by the blower motor with blower switch motor in HI position in HI position equals 3 3 volts 1 8 Waits 6 6 volts 18 Watts _ 8 7 volts 180 Watts 212 volts 1800 atts Advanced Electronics Study Guide 13 How much voltage is dropped at R 1 with blower switch in MED position 0 volts 4 2 volts 6 3 volts 12 volts defective r
4. e um e e a pm ON Voltaic Sensor Voltaic Sensor PV B 21 T ae Powertrain c E Powertrain i e Control Control i E Module i 2 Module i Sensor i aenor I PCM ee MEGA a le d tas greats Lr PE RE C The photovoltaic sensor produces output voltage based on the amount of light 24 2004 2006 Melior Inc Advanced Electronics Study Guide Outputs In modern automotive applications computers control many and sometimes most of a vehicle s functions The commands that come from the computers are called outputs Outputs are the voltage and current signals that operate the actuators which directly control the vehicles operation Some typical examples of actuators include e Relays Solenoids Ignition coils Motors Valves Lamps All of the actuators in automotive applications fall into one of two possible control categories switched or variable Switched applications of which there are two are either on or off e g relays However the two types of variable applications change continuously throughout their operating range These four categories break down as shown here e Switched Voltage on off Switched Ground on off e Constant Frequency Pulse Width Modulated variable e Variable Frequency Pulse Width Modulated variable Switched Voltage A switched voltage control is either on or off and is computer activated by applyi
5. BASE Bi polar transistors are composed of the same N type and P type materials used in diodes Unlike a EMITTER COLLECTOR EMITTER COLLECTOR diode a transistor has three layers of material and two barrier regions arranged either as an NPN type BASE BASE or as a PNP type Bipolar transistors Transistor Construction In this figure the basic construction of the two bi polar transistor types is shown along with the corresponding symbols for each Although their construction is different both NPN and PNP transistors have the same three parts known as the Emitter the Base and the Collector To determine from the symbol which type you have notice that the arrow points toward the base in on a PNP type and toward the emitter out on an NPN type Therefore the rule to keep in mind is that the arrow always points to an N material The arrow also indicates the direction of current flow through the transistor using conventional flow theory NPN transistors tend to be more commonly found in automotive applications than PNP transistors Field Effect Transistors operate differently than bi polars and have different names for the sections FETs have a gate base a source emitter and a drain collector to distinguish them from other types Transistor Operation For our discussion of transistor operation we ll use an NPN component as our example In an NPN transistor the emitter is an N material and the base is a P material The Emitter Bas
6. DVOM Simply put as the requirement for fuel increases the average voltage will increase Ignition Module and Idle Control Motor outputs are additional examples of computer signals with both varying frequency and duty cycle Hot In Run and Start Hot In Run and Start Evaporative EVAP Emission Canister sated Fuel Fuel Fuel Vent Canister Injector 4 Injector 6 Injector 8 Valve err EN EN TUA SPINE tra kere Pon ene p id Powertrain Owertr aln Evaporative 1 Control Canister Control pee mmm m ee mo mmi Rim cm idm el mc ce So rc m Module I Vont Canister Module Valve Control Fuge dw i Fuel Fuel Fuel Fuel i a Control 4 Injector 2 Injector 4 Injector 6 Injector 8 I F hus Driver Driver Driver Driver I Constant Frequency Pulse Width Modulation left Variable Frequency Pulse Width Modulation right The number 6 fuel injector is energized Portions of materials contained herein have been reprinted with permission of General Motors Corporation Service Operations License Agreement 0410610
7. computer 2 Connect a voltmeter between Battery power and the input terminal of the computer 3 Check that the voltmeter reads 12 V If not then the computer is bad Digital Signals 130 Digital inputs are similar to switch signals in that they only have two states on or off What makes digital signals different however is that they cycle many times each second to form a square wave Digital inputs may have a constant duty cycle each on off cycle time is the same or the on off times may 10 vary to signal a change vehicle operation This figure shows 20 digital signals with both varying and constant duty cycles JUU UU L TIME TM Examples of digital input signals include Hall Effect type 20 Crankshaft Position Sensors or Mass Airflow Sensors ET mel LI LSU TIME 2 Digital Signals 19 2004 2006 Melior Inc Advanced Electronics Study Guide Variable or Analog Signals Unlike Digital signals Analog signals vary throughout a voltage range rather than just provide on or off states Typical voltages range from 0 1 V 0 5 V and 0 12 V Analog sensors will fall into one of two categories Variable Resistance or Variable Voltage Variable resistor sensors will be one of four types Thermistors for temperatures Rheostats for levels Potentiometers for position Pressure Transducers Thermistors A thermistor is a heat activated variable resistor that receives a 5V source through a curren
8. drop across a diode does not increase with an increase in applied voltage Diodes are rated in volts not in ohms and should therefore not be tested with an Ohmmeter even though this is a common practice for many technicians Test Procedure Using a meter with a Diode test position check the diode s forward bias voltage red lead on the anode and black lead on the cathode and ensure that it is the same as the device s rating 5 to 7 V for standard silicon for example Reverse the leads and the meter should read OL or its absolute highest resistance value If the diode shows a voltage reading in each direction or OL in both directions it is bad 2004 2006 Melior Inc Advanced Electronics Study Guide Transistors A second type of semiconductor device found in automotive applications is the transistor Transistors can be used as switches to turn circuits on and off or as amplifiers to control a variable current output In the simplest sense a transistor can be seen as a resistor whose value decreases as the electrical input increases Transistors fall into one of two primary categories Bi polar or Field Effect Transistor FET Both types are designed to control output current but bi polars operate based on input current while FETs operate on input voltage EMITTER COLLECTOR EMITTER COLLECTOR Since the bi polar transistor is most commonly used in automotive applications we will limit our discussion to it BASE
9. while the vehicle is operating and allows them to be read with scan tool When an ignition key is turned off all of the information in RAM must be transferred to a different kind of memory to prevent its loss when power is removed Read Only Memory is programmed at the factory and usually contains the basic operating instructions for the computer to function ROM information cannot be changed once the programming is done and it does not require any action on the part of the technician Programmable Read Only Memory is a form of ROM that can be reprogrammed with the proper equipment at the factory PROMs carry the calibration information for vehicle engine transmission operation and can be replaced by the technician The PROM is often referred to as the computer chip When a vehicle is turned off current information in RAM is transferred to PROM memory Electrically Erasable Programmable Read Only Memory is the newest form of computer memory and can be recalibrated by a technician with a scan tool Some technicians may have already done EEPROM updates or flash calibrations to correct a driveability condition or in response to a Technical Service Bulletin Serial Communication In addition to controlling the vehicle s functions automotive computers also need to communicate with each other They do this by sharing serial data on a single wire SOROR Camper that connects the computers Serial data is groups of ones and
10. working voltage Any C C C number of capacitors in parallel will have the same working voltage as the capacitor with the lowest working voltage rating Figure 3 16 Capacitors in parallel Note It is always a good idea to discharge any capacitor by touching the leads together before connecting it to a circuit or meter _12 2004 2006 Melior Inc Advanced Electronics Study Guide Applying Capacitors for Noise If a noise or pop occurs in the audio system when a switch or contact is deactivated capacitors can be used to filter out the noise Referring to the diagram below the first 47uF capacitor will be placed across the switch contact 1 to absorb any surge current at deactivation If the pop is gone you re finished If not place a second capacitor leaving the first from the positive side of the switch contact to ground 2 and test again This capacitor will filter out noise on the power side If a problem still exists insert the third capacitor between the switch and load to ground 3 This capacitor will filter out noise on the load side of the switch 4H12V 12V 12V Customer Activator Swi Direct Switch Activated Device Relay Activated Device Adding capacitors to eliminate popping noises 13 2004 2006 Melior Inc Advanced Electronics Study Guide Module 2 Computers In recent years automotive computers have shown up areas from engine control to air conditioning and everywh
11. 0ms DIV A typical Class data waveform as it appears on an oscilloscope 16 2004 2006 Melior Inc Advanced Electronics Study Guide Hot at all Times B Data Link Connector 15 14 5 4 9 Serial Serial Data Data UART Class 2 Powertrain Control Module ART Multi Radio Instrument Air HVAC Trip ABS Disc Panel Bag Control Calculator Module CD Cluster Module Player ao 1 POWERTRAIN ra svota 777771 P a syoda 77777771 KEYLESS 1 5 VOLTS CONTROL i MODULE ENTRY REGULATED 1 MODULE i DATA i DATA LIME Sun o PEM uuu S P DATA LINE AP 1 P s DATA LINE 1 DATA LINE L 1 OUTPUT 1 i i E E E H E l AX dish BATALINK 9 CONNNECTOR ee CE D a de a i TT S VOLTS F 5wvaLTS 1 AIR BAG PROGRAMMER i MODULE 1 DATA LINE l TA UHE DATA LINE 4 Zr aM DATALIME ATEL DATALIME c UTITUR dt i OUTPUT 1 1 3 Computer data line inputs and outputs 172 2004 2006 Melior Inc Advanced Electronics Study Guide Computer Output Testing If an input sensor or an output actuator is inoperative and the computer is suspected perform a preliminary voltage test on the computer before replacement In this example a voltage measurement of zero at
12. STODAY S CLASS Advanced Electronics Study Guide 2004 2006 Melior Inc Course Objectives Upon completion of this course technicians should understand and be able to apply their knowledge of Concepts applications and components of automotive electronics Measuring and interpreting analog and digital signals pulse width modulation computer inputs and outputs e Semiconductors standard diodes zeners LEDs and transistors e Semiconductor circuitry rectifiers regulators indicators and control devices Automotive computer systems memory and memory types communications and Class ll data System actuators switched and pulse width modulated controls Performance testing for all inputs and outputs Input devices switched analog and digital signals Test procedures Using the Job Sheets As you proceed through the online modules on some pages you will find links that will open a window with a printable procedure or job sheet containing hands on lab activities based on the NATEF standards related to the content you are studying When you come upon a procedure or job sheet link click on it and print the job sheet for completion in the shop See your instructor for guidance in completing the job sheets Some jobs sheets will require supplemental materials such as a vehicle service manual equipment manual or other references Module 1 Overview Semiconductors are a group of devices that are in a normal state n
13. al increases in the applied voltage Any applied voltage greater than the barrier voltage of the diode will be dropped across the load a bulb in this case Varying Source Voltage Below the barrier voltage no current flows Varying Source Voltage Varying Source Voltage Above the barrier voltage current flows Additional voltage is dropped across the load 2004 2006 Melior Inc Advanced Electronics Study Guide Reverse Bias If a diode is inserted into a circuit with the N material connected to the plus side and the P material connected to the negative side it is said to be reverse biased and will not conduct We will later see that some diodes are intentionally installed this way to control current flow and provide circuit protection when loads are turned off There is also a limit to the amount of reverse bias voltage called Peak Inverse Voltage or PIV that a device can tolerate If a voltage is applied that exceeds the PIV the device may be destroyed and require replacement When replacing a diode make sure the PIV rating is sufficiently high to fulfill the current requirements A reverse bias application is shown in this circuit waring Source Woltage No current flow across load Zener Diodes Zeners are a special type of diode that is designed to be installed in a reverse biased configuration and is used as voltage regulator or controller If a Zener is inserted into a circuit in a forward
14. aluminum foil That is the basic construction of a capacitor There are two types of capacitors electrolytic and non electrolytic Electrolytic capacitors have both a positive and negative end while non electrolytics can be inserted in either direction The symbol for an electrolytic capacitor is dc and for a non electrolytic Since the plates a capacitor do not touch it acts like an open in a circuit and will not pass DC current Electrical Charges on capacitor plates Units Capacitors are rated in terms of their storage capacity called Farads as well as their working voltage The Farad F is a measure of the number of electrons a capacitor can store and Capacitors are rated in mucrotarads is very large Most applications will be rated in microfarads mf or nanofarads nf and working uF or nanofarads nF A microfarad is one millionth of a volts DC farad and a nanofarad is one billionth of a farad When selecting a capacitor for a given application make sure the working voltage rating is higher than the source voltage to prevent damage Capacitors in Parallel If two or more capacitors are placed in parallel in a circuit figure 3 16 the total capacitance is determined by adding the individual capacitor values as shown by the equation C1 1 C2 Parallel Therefore two 1000 uF capacitors in parallel have a total e Ll of 2000 uF capacitance Keep in mind that combining capacitors does not increase the
15. ate electrical components ESO susceptible components may ar may not be labeled with the ESO symbol Handle all electrical components carefully Use the following precautions in order ta avoid ESO damage Touch a metal ground order ta remove your body s static charge before servicing any electrical component especially after sliding across a wehicle seat Do not touch exposed terminals Terminals may connect to circuits susceptible ta ESO damage the following actions unless required by the diagnotic prodecure or grounding the components or connectors Connecting test equipment probes to components or connectors Connect the ground lead first when connecting test probes Ground the protective packing of any components before opening Oo mot rest solid state components on metal workbenches or on top af TS radios or other electrical devices Electrostatic Discharge Notice Semiconductor Construction Semiconductors start out as either pure silicon or pure germanium Other elements such as boron or phosphorus are then added to those substances in a process called doping Doping causes a change the electrical properties of the base materials and forms two new substances we will call N material and P material N type material gets its name because it has an excess of electrons or negatively charged particles Likewise P type materials have a shortage of negatively charged el
16. biased configuration it will behave exactly like a standard diode The symbol for a Zener diode is different from the standard diode symbol as shown in this illustration Zener diode symbol Zeners are manufactured in such a way that they have a certain breakover voltage or Zener point The Zener point is the amount of reverse bias voltage that must be applied to the device to make it conduct current Once the breakover voltage is reached the voltage drop across the Zener will not increase even if the applied voltage is increased For example if a six volt Zener is placed in a parallel circuit with a series lamp with 5 volts applied all of the voltage will be dropped across the Zener and the bulb will not light since the breakover voltage has not been reached Applying seven volts to the same circuit will show a six volt drop across the diode and one volt across the lamp Increasing the applied voltage to 10 volts we find the voltage across the Zener remains at its rated six volts but the lamp voltage is increased to four volts This operating characteristic is what makes Zener diodes useful as voltage regulators in applications such as generators and power supplies 8 1 V Diode 6 1 Y zener Diode Series circuit with 6 1V Zener diode 2004 2006 Melior Inc Advanced Electronics Study Guide Light Emitting Diodes LEDs Light Emitting Diodes conduct when forward biased and block current flow when reverse biased ju
17. e computers voltage inputs and P aci i T OUTPUT grounding inputs If a sensor has an sev LL CONTROL external power feed it will connect to a 2 grounding input Likewise a sensor with SOLID STATE e an external ground will be applied to on Apo 6 internal voltage Note that both types of 5V inputs use internal resistors to limit the current and protect the electronics Both types of inputs will be covered in more detail in the next module e Output Control these are the output drivers that operate the actuators by turning them on and off Most actuators are controlled by applying or 14 222225 2 2222222222222222 2 1 2 2414 5 ground however some outputs control Typical Computer the applied voltage as is the case with fuel pump relays INPUT rl lE E Se eee eee Ss Se SS Computer Memory Automotive computers have four basic forms of memory e Random Access Memory RAM e Read Only Memory ROM e Programmable Read Only Memory PROM e Electrically Erasable Programmable Read Only Memory EEPROM Random Access is the only volatile form of memory which means that it will clear if the power is removed RAM has two functions in an automotive application 1 It stores information from the sensors while it calculates the actions it needs to take and 14 2004 2006 Melior Inc Advanced Electronics Study Guide 2 It stores the diagnostic codes
18. e junction is like that in a diode meaning that for a silicon based transistor if the voltage between the base and the emitter is 5 to 7 V it will conduct and current will begin to flow As the Emitter Base E B junction conducts the resistance of the Emitter Collector E C begins to drop and current begins to flow through the transistor thus turning on the circuit Further increasing the base current reduces the Emitter Collector resistance even more and produces an increase in the circuit current Notice also that base current flows into the base and out the emitter while the collector current enters the collector and exits the emitter Therefore the emitter current is the sum of both the base current and the collector current or I lp Ic When selecting a transistor for use make sure the current ratings are sufficient to handle the circuit requirements A PNP transistor will operate the same as an NPN except the base will be at least 7 V lower than the emitter rather than higher 2004 2006 Melior Inc Advanced Electronics Study Guide Applications In a transistor being used as an amplifier small variations to the base current will correspond as much larger outputs at the collector If however base current is not varied but is toggled between high current saturation and off then the transistor becomes a high speed switch for On Off applications A saturation switch can also be compared to a relay in that it u
19. e rectification of one full cycle is described in the following section Rectifier Operation During the first half cycle of an AC wave point A is Di no positive and point B is negative Beginning at point A and using conventional flow we find that the positive pulse sees D2 as forward biased and D1 as reverse biased and passes through D2 After passing through D2 we find that D4 is also reverse biased and the aad current moves through 1 and around to the junction of D1 and D3 D1 will not conduct since it has positive voltage on each side but D3 is forward biased and the circuit is completed back to point B bypassing D4 which also has positive voltage on each side 03 04 R1 Diode Rectifier Bridge 1 half cycle On the second half cycle point A is negative and point B is positive Current will flow from point B through D4 through R1 in the same direction as the first half cycle through D1 and back to point A This application is called a Full Wave Rectifier and results in the type of output shown on the next page The signal in the illustration which is labeled as input is the basic AC produced by a single winding in a generator The output signal is the same wave after it has been converted in a full wave rectifier These two signals are for one phase only and are measured across the resistor R1 The actual total output of a generator will have three identical phases each 120 degrees later than the previo
20. ected should be B and vice versa Also note that the actual input the computer uses is read across the internal resistor rather than the switch itself As shown here the voltage across the internal resistors for both of these switches varies with the operation of the switches Open Closed AIC Compressor Refrigerant Pressure Switch Opens at 2 9 PSI Closes at 22 32 A C Compressor Refrigerant Pressure Switch Opens at 2 9 PSI Clases at 22 32 PSI e e e e e Brake Switch i I I I 5 Switch oy AIC Low 207 Input 4 p COM LU i Pressure 2 Pressure Cut Off L Powertrain Cur un Powertrain Switch Control Switch i Control Signal Module Signal Module i DONI 1 PCM 4 I a 1 Typical Input Switches Switch Input Testing If a switch input is not functioning and the switch itself is found to be operating properly then a suspected computer failure can be tested as follows For externally grounded switches 1 Remove the switch connecting wire from the computer 2 Connect a voltmeter between ground and the input terminal of the computer 3 Check that the voltmeter reads 12 V If not then the computer is bad For externally powered switches 1 Remove the switch connecting wire from the
21. ectrons and are thus more positive If we join one N material and one P material we create a P N junction which is the basic building block of all semiconductors N TYPE P TYPE Semiconductors do not conduct well in their MATERIAL MATERIAL normal state that is they have a high resistance when no voltage is applied Conductors on the other hand will exhibit a low resistance even if unpowered However when a voltage is properly applied across a P N junction the internal resistance of the device decreases and the current flow increases The minimum voltage required to allow current to flow across the junction is called the Barrier Voltage P N Junction The barrier voltages for different components will vary depending on the basic material used in the construction of the device and the substances used in the doping process For our purposes we will use the most common barrier voltages of 5 to 7 volts for silicon based components and 3 to 5 volts for germanium components Diodes Diodes are the simplest of all semiconductors and have only one P N junction or barrier region That is to say they have one N material section connected to one P material section Diodes serve a number of functions in automotive circuits including rectification voltage spike protection and indicator lighting Those that give off light are called Light Emitting Diodes LEDs and all will be covered later 2004 2006 Melior Inc Advanced Electronics
22. either good conductors nor good insulators From our earlier study of electrical fundamentals we recall that good conductors have only one or two electrons in the outer shell while insulators have many more around eight Semiconductors usually made of silicon or germanium tend to have four outer shell electrons and have the unusual characteristic of becoming conductors as voltage is applied Although there are many types of semiconductors also called solid state devices we will limit our discussion to the two most common types diodes and transistors Electrostatic Discharge The electrostatic charge that can build up on your body and discharge to another object such as a doorknob is in excess of 50 000 volts That static discharge is enough to destroy many of the semiconductor components you may come into contact with in automotive systems In order to prevent damage to components look for the Electrostatic Discharge ESD symbol shown in the box below and carefully follow the instructions on handling those devices In addition any electronic parts or components shipped in a dark blue or black anti static bag should be left in the bag until they are ready to be installed Electronic components can be easily protected against accidental damage by following these few simple precautions 2004 2006 Melior Inc Advanced Electronics Study Guide Handling Sensitve Parts Motice Notice Blectrastatic Discharge ESO damage solid st
23. el Level sensor is a good example of a rheostat As the amount of fuel in the tank decreases the resistance and voltage drop of the sensor changes which varies the voltage drop across the internal resistor where the input is measured Be aware that some Fuel Level sensors will have a higher resistance with low fuel and some will have a lower resistance with low fuel Refer to the appropriate service manual 20 2004 2006 Melior Inc Advanced Electronics Study Guide Powertrain Sere m Gia Powertrain EET Control 1 Control 1 n Module i Sensor Module Sensor PCM Signal T PCM Signal a E usas mca 4 ee te a Level Level Sender Sender Unit Unit l Black CP MISERE EE S Powertrain EO SINGEN S Powertrain Control 1 Control i E Module I TM Module COS l PCM l PCM i Ground i Ground um e e e e e MO GG UN d e le p hiss The rheostat mechanically varies the resistance and voltage drop Potentiometers Potentiometers are three wire position sensors that have 5 V ground and input signals all tied into a computer Like rheostats pots are also mechanically variable as opposed to changing by temperature pressure or light However rather than altering the voltage drop across an
24. elay will Keep the blower motor from operating in LOW speed speed MED speed _ All speeds The voltage drop at R 2 with blower switch in LOW position will equal 0 volts 4 2 volts _ 4 3 volts _ 12 volts 14 If S 104 has high resistance how will voltage drop at the blower motor be affected It will qa down Itwill qa up twil be unchange _ Mone ofthe above 2004 2006 Melior Inc Advanced Electronics Study Guide Exercise answers 1 2 8 2 1 8 O 3 8 O 4 30 amps 5 4 2 amps 6 6 6 amps 7 30 amps 8 4 2 volts 9 O volts 10 4 2 volts 11 12 volts 12 180 watts 13 speed 14 It will go down Capacitors Capacitors are devices that store electrical charges and behave like temporary batteries Technicians may have Capacitors store electrical charges seen them used as filters on alternators or radios to reduce and act like temporary batteries noise or even in older point style distributors as condensers By controlling how quickly they charge and discharge we can also use them as timers Capacitors basically consist of two metallic plates separated by an insulator called a dielectric Dielectrics can be something as simple as a piece of paper A simple capacitor can be made by placing a sheet of paper between two equal sized sheets of aluminum foil Wrap all three sheets around a paper towel roll don t let the aluminum sheets touch and attach a connector wire to each piece of
25. ere in between They control engine performance and emissions operate the Anti lock brakes shift the transmission adjust the suspension and in some vehicles control the radio Ironically these electronic wonders are often credited with capabilities they don t have and blamed for problems they didn t cause A simple understanding of what automotive computers do and how they work will greatly assist in helping the technician diagnose and repair microprocessor based systems First of all computers do not think They are just machines with some very small parts that take information from sensors apply that information to an internal microprocessor program and then tell some device to turn on or off Computers also have memories for storing diagnostic codes power supplies for sensors and communications capabilities for sharing information with other computers Computer Features Automotive computers as shown in this example tend to have the same general features even though they control different systems From this illustration we can see the following Memory shown here as an EEPROM they have both long term and short term memories e Voltage Regulators the regulators take the 12 V input voltage and convert it to other lower voltages Those voltages can then be used to power input sensors 5V or to operate the internal electronics e Inputs this illustration shows both types of inputs used by automotive eee e
26. internal resistor as variable resistor sensors do potentiometers actually send a voltage signal directly to the computer These sensor inputs supply information on the position of throttle valves EGR pintles etc The sensor signal voltage is applied to the computer through a current limiting resistor to ground Notice also that potentiometers do not use limiting resistors in the 5 volt supply line Some common examples of potentiometers include e Throttle Position Sensor e EGR Position Sensor e Accelerator Pedal Position Sensor e Air Door Motor Feedback Sensor HVAC n e e e e e pee eee ee eee eee Powertrain Powertrain i i Control 1 I Control i Module Module i SW i A 54 i PCM eee RE E m e um um Bm me mom a p S hud Throttle Throttle Position Position Sensor Sensor TPS TPS pom Powertrain p Poweria i Signal I 1 Signal i ema 1 Sensor Sensor i odule Sensor 1 PCM i Sensor 1 PCM l Ground i Ground i 4 hus hess The potentiometer sends a variable voltage signal to the computer Pressure Transducers Pressure Transducer sensors have the same computer connections as potentiometers The difference is that pressure sensors operate based on a change in pressure rather than a change in position Diagnosis and testing of pressure sen
27. ive purge valve in the next illustration will be cycled at 35 Hertz HZ or 35 times each second If the duty cycle during that time is 5096 the average voltage will be 6 Volts and the valve will open approximately half way At this setting it will flow at one half of its vapor capacity for emissions control Changing the duty cycle to 25 about 3 volts average reduces vapor flow to one fourth of capacity but the on off rate remains at 35 times per second The same concept applies if the duty cycle increases to 7596 Similar to the evaporative valves transmission pressure control valves control line pressure and EGR valves control recirculation gas using constant frequency PWM signals 26 2004 2006 Melior Inc Advanced Electronics Study Guide Variable Frequency Pulse Width Modulation Some output actuators must change operating frequency in response to changing engine or transmission speed As a result these types of actuators cannot use constant frequency computer outputs Refer to the fuel injector circuit below Although injectors are still controlled by a cycling ground their demands change with engine speed and their on off times are sequenced to coincide with Crankshaft Position Sensor inputs That means they must change both how often they open and how long they stay open Even though injectors may have a large demand at slower engine speeds or lower demand at higher speeds their average voltages can still be measured with a
28. llector current of 2500 mA and a gain of 200 then dividing the collector current by the gain gives the highest base current that can be used In this case 2500 mA 200 12 5 mA maximum base current Technicians should consider all these factors when doing repairs to ensure the transistor has the necessary capabilities 2004 2006 Melior Inc Advanced Electronics Study Guide Collector Current lirnmeter 2000 mA Gain I 20 m E Gain 100 Gain formula Transistor Testing The testing of transistors is a simple process but just as with diodes it is often done incorrectly As we did before we ll use an NPN transistor for our example to show the six possible checks To make the process easier look at transistors as two diodes connected back to back An NPN transistor is then just two P N junctions one between the Emitter Base and one between the Base Collector Some of the connections will be forward biased and some will be reverse biased Use the diode position on a DVOM just as if you are measuring a diode and it will be easy Do not use an ohmmeter since different meters will give different and sometimes erroneous results The six tests on a silicon based NPN will be as follows 1 Red lead on the Base P and the Black lead on the Emitter N the meter should read approximately 5 7 volts 2 Black lead on the Base P and the Red lead on the Emitter N the mete
29. n the inside of the sensor and is compared to atmospheric oxygen The O2 sensor signal is evaluated inside the PCM based both on voltage output and its transition rate from high voltage to low voltage E Oxygen Sensor i B i 3 T P3 Exhaust i System Exhaust System xygen Sensor D 7 a d a Rn Li ET g Low oxygen content rich produces a low voltage signal high oxygen content produces a higher voltage signal Photovoltaic Sensor The photovoltaic sensor is similar to the photoresistor only in the sense that it is affected by light While the photoresistor changes its resistive value the photovoltaic sensor actually produces an output voltage that can be used by a computer to determine the intensity of sunlight Photovoltaic sensors are commonly referred to as Sun Load Sensors and are primarily used with A C systems to determine heat load Photovoltaic sensors can also be used to turn on headlights at dark operate an auto dimming rear view mirror or operate interior light functions A photovoltaic sensor can be tested by exposing it to varying amounts of light and measuring the voltage output mm Powertrain Powertrain Control Control 1 Module Sensor Module Sensor copre i Signal I Signal um um mm jm mm m m
30. ng or removing a voltage source Refer to the fuel pump circuit below In this typical fuel pump circuit the relay coil has a fixed ground and the PCM supplies the 12 Volt power to energize the coil engage the contacts and supply power to the pump Some applications of relays solenoids lamps valves and motors are switched voltage activated Powertrain Pump 1 Control Pump Relay Module Relay Control PCM Control hus 2 Powertrain Control Module PCM amp Fuel Pump Relay Fuel Pump Relay Switched Voltage Control Switched Ground Like switched voltage applications switched ground devices are also either on or off In the following illustration the transmission shift valves have a constant 12 Volts on one end and are controlled by ground signals from the PCM on the other In automotive applications switched ground control is much more common than switched voltage applications due to a reduced possibility of arcing Relays solenoids lamps valves and motors can all be ground switch controlled 25 2004 2006 Melior Inc Advanced Electronics Study Guide Hot In Run and Start Hot In Run and Start 2 3 Shift 1 2 Shift 2 3 Shift 1 2 Shift Solenoid Solenoid Solenoid Solenoid 3 Powertrain i Fo Y Powertrain I 7 Control i ENE Control Qo 2 3 Shift 1 2Shift 1 2 3 Shift 1 2Shift Module EN 1 Oe UM j L
31. point A to ground may be a computer failure or it may be a shorted sensor or wire To determine which remove the wire from the computer at point A and insert a 50000 resistor between point A and ground If the voltage at point A is still zero the computer is bad If there is now a voltage at point A the sensor or wire is the problem To check a computer output suspected of failure remove the connecting wire from the computer and insert a gt 500 mA bulb between the output and 12 volt power Activate the output usually with INPUT a scan tool and check for operation of the bulb If the bulb lights the actuator is the problem if not the computer has failed Caution Be very careful performing this test with a test light Many test lights draw far more than and will damage the computer Typical Input Sensor Fault Protection In addition to protecting against Data Line problems modern automotive computers monitor current and voltage on input and output wires If a failure wire or component causes the amperage or voltage in a particular circuit to be too high the computer will disable the line to prevent internal damage Some applications will also disconnect for voltage current failures that are too low for instance if an injector is disconnected Inputs Automotive computers always need to know the most current operating conditions of a vehicle to determine what changes should be made This operating information i
32. r should read OL no conduction 3 Red lead on the Base P and the Black lead on the Collector N the meter should approximately 5 volts 4 Black lead on the Base P and the Red lead on the Collector N the meter should read OL 5 Red lead on the Emitter N and the Black lead on the Collector N the meter should read OL 6 Black lead on the Collector N and the Red lead on the Emitter N the meter should read OL Testing for PNP transistors is similar and just as easy if you keep track of which junctions are forward biased and which are reverse biased The Emitter Collector junctions should always read OL 2004 2006 Melior Inc Advanced Electronics Study Guide Transistor Circuit This is a simple transistor circuit using a capacitor and a load bulb Study the schematic to determine the circuit s function What might this circuit be used for in an automotive application When the switch is closed a voltage is applied to the base circuit that is sufficient to make the transistor conduct A ground is then provided through the transistor to the bulb which lights since it has full time power The capacitor also charges when the switch is on If the switch is turned off the capacitor discharges through the base circuit and the transistor continues to operate the bulb until the capacitor is depleted This particular application could be used for interior lights dimming sometimes called theater dimming
33. s Lontro dus dius Switched ground control 1 2 Shift Solenoid is switched on at right Pulse Width Modulation Volts Pulse Width Modulation PWM is a control method 100 Duty Cycle in which a computer produces a variable or partial ii 12 volts average operation of a device by supplying a constantly cycling ground signal to the device As seen in this illustration the average voltage applied to a device is dependent on the Duty Cycle of a PWM signal Time Duty Cycle is the amount of time a signal is turned on as compared to the total amount of operating Volts time For example if a signal has 100 duty cycle 20 50 Duty Cycle its average voltage will be 12 volts and the actuator 6 volts average will operate at full capacity Changing the output to a 50 duty cycle on half the time off half the time drops the average voltage to 6 volts and the speed mme or intensity of operation decreases Even though PWM signals are digital the output can Volts be measured with a DVOM using the average 20 23 Duty Cycle voltage readings EX 3 volts average I ll ll PWM Duty Cycles Constant Frequency Pulse Width Modulation The first type of Pulse Width Modulated signal is the Constant Frequency output Constant frequency signals as the name implies turn an actuator on and off the same number of times each second The computer then varies the duty cycle to alter the open close time For example the evaporat
34. s fed to the computers from a series of inputs called sensors Sensor signals come in a variety of types but all generally fall into one of three broad categories Switches Digital Signals e Analog or Variable Signals Switches owitches are the simplest type of sensors and provide the computer with information that a device is on or off open or closed high or low etc In the closed position a switch may send a voltage usually 12 V to the computer or it may provide a ground For example a brake switch may send a 12 V signal when pressed and a 0 V signal when released A computer could then use that information to disengage a Torque Converter Clutch or engage the Anti Lock Brake system Some examples of switches include Door Jamb Oil Level Transmission Ranges Torque Converter Clutch Oil Pressure Park Headlights Closed Throttle A C Pressure Transmission Pressure Blower Speeds 18 2004 2006 Melior Inc Advanced Electronics Study Guide Notice in this illustration that the A C compressor switch 15 externally attached to ground while the TCC brake switch is fused to the Battery B When each switch is closed the A C compressor signal feeds into the computer through a limiting resistor to B and the TCC switch connects through a limiting resistor to an internal computer ground In this way if a technician knows a particular switch is connected to ground then the signal from the computer with the switch disconn
35. ses a small current to control a large current However a transistor has only three legs compared to the relay s four Transistors also contain no moving parts Base Current Collector Current Collector Current Base Current Emitter Current Transistor Currents Current Limiting Refer to the schematic at right and notice the 1KW resistor in the base circuit This resistor serves two purposes first it limits the amount of current that flows through the base circuit and protects the transistor from damage and second it is the output controller for the Emitter Collector circuit AS we increase or decrease the amount of base current by changing the base resistor we control how much the transistor turns on This will limit the Emitter Collector current which protects the transistor The resistance of the lamp also serves to limit the E C current when the transistor is operating Gain Gain is a factor that affects the operation of a transistor and must be taken into account when selecting a replacement component There are no units associated with gain such as volts or amps it is simply the ratio of the collector current compared to the base current For instance if a transistor has a gain of 100 then 20 mA of base current will yield 2000 mA of collector current Simply multiply the gain times base current to get the collector output Gain can also be used to calculate maximum base current If a transistor has a maximum co
36. shown here with a list of typical pin identifications ee 214 cm ci BE G3 O If a serial data failure is suspected a simple voltage secondary UART 8182 Baud Serial Data 800 Secondary Class 710 or 160 Baud Serial Data 1995 only 461 41850 Bus L Line 2 Wire Systems or Single Wire Class 2 1807 Ride Control Diagnostic Enable CKT 1826 Chassis Body Ground Pin CKT 150 a Signal Ground Pin 451 PCM VCM Diagnostic Enable 448 K Line for International Standards Organization ISO Application Keylass Entry Enable 1455 or Theft Diagnostic Enable 477 Primary UART 1061 41850 Bus Line for J1850 2 Wire Applications 11 Electronic Variable Orifice EVO Steering 1294 or Magnetic Steering Variable Assist MSVA ABS Diagnostic CKT 798 or CCM Diagnostic Enable CKT 555 SIR Diagnostic Enable 326 E amp C Bus 835 L Line for International Standards Organization ISO Application Battery Power from Vehicle 4 MAX test on the data line will validate its operation Check 2V DC 10 1 200mV DC 1 1 the DC voltage on the Data Link Connector between pins 2 and 5 with the vehicle operating The DVOM should measure approximately 2 V to 7 V A reading of 7 V indicates a short to power and a reading V is a short to ground 2
37. sors will be basically the same as for any input potentiometer Common types of pressure sensors include Manifold Absolute Pressure MAP for measuring engine load Fuel Tank 21 2004 2006 Melior Inc Advanced Electronics Study Guide Pressure FTP for checking fuel tank vapor pressure as part of emissions testing and the A C pressure sensor for measuring air conditioning high side pressure Or _ Powertrain Powertrain Control 1 Control Module Sensor Module 1 s Sensor PCM 2 I Signal PCM Signal M c Manifold Absolute Pressure Manifold Absolute Pressure Sensor Pressure Change Pressure Black Change Powertrain Ar rptu es TERRA Les rae TE RE Powertrain 1 Control i Control PE Module a Module Sensor PCM Sensor Ground l Ground 4 e e e e e e e e e e e e d e mm e e e e um um um um um d hiss Pressure transducers operate based on a change in pressure rather than a change in position Photoresistors One last type of variable resistor we need to mention is the photoresistor Photoresistors are wired to computer modules in the same way as thermistors or rheostats The difference is the photoresistor changes its resistance based on how much light strikes its surface rather than on temperat
38. st like standard diodes The two primary differences between LEDs and standard diodes are that LEDs emit light when they begin to conduct and the forward bias voltages for LEDs are slightly higher about 1 5 to 2 5 volts A resistor usually 470 ohms must also be used in series with an LED to limit current typically 20 30ma and prevent damage to the device The symbol for an LED shown here is a standard diode symbol with two arrows pointing outward to signify that it gives off light Do not confuse this symbol with one that has arrows pointing in That is the symbol for a photodiode that conducts when exposed to light Because they turn on and off more quickly LEDs are typically used as indicator lights instrument panels more recently as rear 4 park brake lights They consume less energy to operate and create less heat than standard bulbs Light Emitting Diode symbol Rectifier A Rectifier is a device used to change AC to DC The most common use of diodes as rectifiers is in the generator Automotive generators produce 3 phase alternating current that must be converted to direct current by a rectifier bridge before it can be used A rectifier bridge is a network of six diodes arranged in such a way that the half cycles of each AC phase are made to travel in the same direction rather than in opposite directions as is typically the case in alternating current Each phase of a generator uses only four of the six diodes and th
39. t limiting resistor from the Powertrain Control Module PCM As a thermistor s temperature increases its resistance and voltage drop decrease This in turn causes the voltage drop across the internal resistor located inside the computer to increase The internal voltage drop then becomes the signal input In addition to a 5V source thermistors also receive their ground source from the PCM i Powertrain eae ky 777771 Powertrain 5V Control i I Contr ol FS l Module Sensor Module 1 Sensor PCM i Signal PCM i Signal I 4 a Socal RA A Jes sai jedi i a 4 4 i AMEE oes Powertrain ws 4 Powertrain i 1 Control i Control i Module i pee i Module dria PCM i Ground I i Ground e eo al AU e OAM e AU ll hus thermistor s resistance and voltage drop decrease with heat Some examples of typical thermistors include e Engine Coolant Temperature sensor Intake Air Temperature sensor Transmission Fluid Temperature sensor Outside Air Temperature sensor Heat Duct Temperature sensor Ambient Air Temperature sensor A C Duct temperature sensor Rheostats Rheostat sensors are similar to thermistors in that they are both variable resistors The difference is that rheostats operate mechanically rather than by temperature A Fu
40. ure or position As the amount of light changes the voltage drop across the photoresistor changes and causes the voltage across the internal resistor to change which determines the input voltage Photoresistors are used to turn on Automatic Headlights at dusk control interior lighting operation and determine heat load for automatic Air Conditioning systems Peewee eee eee ee Powertrain Powertrain Control i re i Control i I Module 3 Sensor i Module Sensor PCM i Signal i i Signal 5 23 1 Ji E ETE IC M d na pt EE Powertrain RS SS SSeS Se Sas Powertrain i I I l Control Control SE nod E Moduls Module l l PCM PCM I Ground i VEENI i Ground i AMAT EE EAE estar aves drin PIRE ERA hus hes The photoresistor changes its resistance based on how much light strikes its surface 22 2004 2006 Melior Inc Advanced Electronics Study Guide Powertrain Control MAF ECT AIT Refrigerant Pressure Sensor B c Throttle Position TP Sensor Manifold Module 5 volt 3 Walt Sensor Sensor bancar Reference B Reference Signal Signal Signal eee SS SS ee eee B A n AY i Engin 7 Pressure l Coolant MAF Sensor ure Sensor A Intake Air Temperature IAT Sensor Powertrain Control TFT Senser EGR Valv Module PCM omm
41. us one as shown Diode Rectifier Bridge 274 half cycle 2004 2006 Melior Inc Advanced Electronics Study Guide NW AC to DC rectification Three phase full wave rectified generator output Clamping Diodes Whenever a current is passed through a device with a coil relay solenoid etc a magnetic field is created around the coil Turning the device off causes the magnetic field to collapse and create an electrical pulse in the opposite direction as the original current flow This pulse is referred to as a voltage spike Voltage spikes can be many times larger than the original voltage that was applied to the device and if not controlled can cause damage to circuits and other electronic components To protect these circuits we use clamping diodes Clamping diodes are standard diodes placed across device coils so as to be reverse biased to current flow in normal operation When the circuit is opened however the resulting spike flows in the opposite direction which now makes the diode forward biased The current continues to flow in a circle dissipating the electrical energy through the coil in the form of heat Opening the switch causes the magnetic field in the coil to collapse a short period Voltage Spike Dissipation Coil Energized Iv uw of time the voltage will completely dissipate Clamping diode to dissipate voltage spike Diode Testing Unlike resistors the voltage
42. zeroes electrical ons Fart om and offs transmitted between computers in a language they can decipher It is also the information including diagnostic codes read by a scan tool Data Transfer Serial Data Link Before 1996 manufacturers used different forms of communication and not all systems were compatible Beginning 1996 a new standard was adopted as part of the OBD II emissions implementation The new standard is called Class 2 and uses a 7 volt line toggled on and off to make ones and zeroes The newest data transmission protocol to be used is called Class C or CAN for Controller Area Network and it will be much faster than Class 2 CLASS 2 TVOLTS 1 0 1 0 PULL HIGH TO TALK VARIABLE PULSE 0 VOLTS WIDTH Class Data Format Modern automotive computers must be able to communicate with each other otherwise they will begin limited operation or stop working all together Some systems such as air conditioning may require several computers to function and the failure of one can cause the entire system to fail If any or all of 15 2004 2006 Melior Inc Advanced Electronics Study Guide the computers will not communicate with each other or with a scan tool then one of four problems is usually the cause They are PONS Loss of voltage to a computer Loss of ground to a computer Data line has grounded or is open A computer has failed internally The 16 pin Data Link Connector DLC is
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