The scan tool and digital storage oscilloscope should be considered
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1. Fig 2A Thinking In Threads At this point we ve collected data and made relationships The next step is to think in threads and or processes to gather enough pieces to reveal the sequences in which they fit and inter act To help put this mindset into action ask yourself these questions 1s what I m observing an action or a reaction What happened before this and what happens after Where does this fit in to the process Variable Reluctance Sensor Minimum 2V Peak to Peak f Signal ECM Triggers on Falling Edge of Signal Corresponding to Fig 2C 38 MOTOR May 2013 Edge of Tooth Moving Away From Sensor Centerline W hat is the pathway for the information energy sig nal What is the input and output Another strategy is to sim ply observe the processes that occur when the system is in operation This is also an important mindset specifically for diag nosis F or example a failure in a system means a broken process Diagnosis is finding where its broken A technique for doing this is to follow the processes of operation H ere s an example of a no crank on a simple starter cir cuit from the learner s perspective The process of turning the key results in a running engine But on the next start we turn the key and nothing happens If we re not familiar with the system we could literally follow the flow of energy by following the wires starting at the b2. ne characteristic of a great automotive tech nician is the ability to perform efficient and effective diagnostics These techs seem to know what they need to know and the tools and tests to get it Of course this is partly due to an accumulation of mean ingful exoerience experience based on real understanding One of the skills that distinguishes an expert is a Knack for finding the relevant details of his diagnostic experiences and making the connections and putting the pieces together These abilities are what lead to an in depth understanding of automotive systems and to meaning ful experience Can we do this for our selves Certainly In this article l m going to present a fundamental framework for the basis of the behaviors that believe will lead us to become diagnostically the best we can be It s based on these elements Goal Become the best can be di agnostically in the shortest amount of time How Learn to put the pieces to gether so can develop an in depth understanding of automotive systems Mindset m not going to spend my career aS a go no go gauge dependent on others l m going to be a diagnostic learning machine Perspective D iagnostics is not just about the fix its about the fix through understanding To accomplish our diagnostic tasks it s important to have the right tools They are the interface between us and our ability to put the pieces together
3. MOTOR 35 x oO O N S a oO On ia D C oO A lt D O fa ia T S oO Cc n Oo aus O jae scope pinpoints the exact components that are failing and confirms those that are still functioning properly Finally a lab scope fills in the blanks not covered by the scan tool The PCM monitors certain aspects of the system The lab scope can be config ured to monitor almost any thing the detail of the wave form offers insights into the details of the system F or ex ample a scan tool reports charging voltage a lab scope zooms in on alternator diode performance H ere s another very power ful way to look at all of this The PCM is connected to the rest of the vehicle only through the electrical circuits as illustrated in Fig 1 All of the smarts to operate the sys tem including the energy and information have to go through the electrical circuits Working without either tool scan tool or lab scope is like working half blind especially when it comes to learning about the system as well as for many diagnostic situations Getting Your Tools Up amp Running expect almost everyone reading this article has access to or owns a scan tool But what about a lab scope It s been said that we re only as good as our greatest weakness If you do have both a scan tool and a lab scope it would cer tainly be unfortunate if the greatest weakne
4. mass airflow M AF sensors orm Jorge Menchu amp wa Illustrations Dynamic Picture To further enhance the capabilities of relationships consider live test data as a dynamic picture of everything that s related to it This is especially powerful for waveforms due to the extreme detail Check out Figs 2A B and C on page 38 Each of these items helps to influence the shape of the waveform or is influenced by it The waveform dynamically relates them H ere s an example of two of these relationships The static description in a manual of a variable reluc tance sensor The waveform brings it alive through its de tailed and dynamic movie of a running waveform The mechanics of the sensor includes its physical parts and mounting The waveform dynamically rep resents the integrity of the sensor wheel profile and the distance of the pickup to the wheel Change any of these variables and the waveform changes In these examples the waveform adds to our understanding of the physi cal parts and supplements the static de scription in the manuals As a result we not only understand the parts and pieces better but we also learn their character and behavior When you think of a waveform from this perspective it s easy to see why it has become such an important part of learning diagnosing and communicat ing just as scan data is essential for un derstanding the strategies and the sys tem s perspective
5. The diagnostic tools on the top of the list are the scan tool and the lab scope What makes these tools particularly valuable is that when used together they give a unique and complemen tary perspective of any automotive sys tem that s being diagnosed right from the system s core information pipeline from the nuts amp bolts that make up the mechanics of the system to the strategies that run it In Fig 1 on page 36 we can see how the scan tool and oscilloscope allow us to un derstand the functions of the PCM 34 MOTOR May 2013 MEINI TNL By JORGE MENCHU The scan tool and digital storage oscilloscope should be considered indispensable tools But they can quickly become nearly worthless if the user doesn t develop an effective way of integrating them into an overall approach to diagnostics the circuit wiring and related circuit components Scan Tool We re all familiar with the scan tool s text discrete values for mat and the smarts that come with us ing it It s a powerful tap into the brain at the center of the automotive sys tem giving us the software s perspec tive In general the scan tool is cer tainly strong on the system strategy side and relatively weaker when it comes to the details of the mechanical side of the system Lab Scope A lab scope taps directly into the information and energy pipe lines of the system the circuits A key characteristic is the extreme detail of fere
6. among vehicle systems We simply don t know what to expect because of shared data among individual vehicle systems T he question is Do we want to learn it the costly way or the easy way Framework A framework is basically the mechanics of the system operation deally the information is found in a func tional diagram such as the one shown in Fig 3 above It s like a wiring diagram without the detail Ideally it s supplied within asystem s theory of operation Functional diagrams typically in clude T he key components involved in the function of operation including net worked devices The relationships of key compo nents to each other their placement T he operational flow of information throughout the system the lines and arrows 40 MOTOR May 2013 Refrigerant Temperature Sensor Compressor On Off A C Compressor Clutch Unfortunately functional diagrams are not always available No problem you can make your own In fact It s worth it to reinforce these thought processes H ere s how 1 Bring together the theory of oper ation and a wiring diagram 2 Pick out the main players of the system and the main variables includ ing the networked connections 3 Draw boxes around the compo nents to construct a logical layout 4 Label each 5 Draw arrows to show the relation _ Framework Fig 4 ships indicating the flow of information And always identify
7. attery and every step of the way to the starter perhaps a voltage test to see if the voltage disappears At some point the broken step in the process will be revealed voltage in and no voltage out or voltage in and no action out A Full Systems Approach To this point we ve discussed the tools and how they re used to gather data N ow let s wrap everything up into a full systems approach The overall concept of the approach is to take advantage of the different levels of information and an alyze them in the way we naturally learn This means following the same steps an engineer uses to design a system Engineer Us Develop an Bec A target for Define the A framework functional to work within building blocks A road map of the system to guide us Get into the details to design and Apply build A C Switch Indicator A C Engine REM Compressor RPM Simplified Control Signal Battery A C Compressor Relay Dual Pressure Switch cu Y TO Circuit Diagram Fig 3 Target Defining the target means developing an understanding of how the system works This information is typically found in a service manual s theory of operation and sometimes in a training module It might include function operation behavior variables requirements and conditions The actu al target is to restore proper operation This is vital today due to high levels of networked integration
8. d by the line drawing format in which even the smallest changes can be crucial information The result is a de tailed insight into the technology s per spective of the system The lab scope is very strong on the technology side and relatively weaker on the strategy side When we combine the characteristics of the scan tool and the lab scope we discover three applicable values They provide different perspectives of the same problem they complement each other s weakness and each tool extends into depths of the system where the other does not For diagnosis the scan tool typically is connected to a vehicle before the lab scope and the scope is used to comple ment the scan data in several ways First it validates the values in the scan data The scan tool interprets the infor mation from the PCM the PCM re ports information from the circuit The displayed values of either one can be in correct The waveform from the scope can be used to validate the quality and values of the signal to the PCM The lab scope also validates expected actions Scan data indicates a command sent to operate an actuator Did it actu ally accomplish this goal The second way the lab scope com plements the scan tool is by pinpointing a problem in a circuit While the scan tool s code points to a problem in a cir cuit the scope s waveform pinpoints it Take for example a code for a high side short in an injector circuit A lab May 2013
9. data line connections Road Map The arrows of the func tional diagram illustrate the basic flow of actions and information within the system Using the road map will keep you focused and on track H ere s how it goes for using a lab scope F ig 4 below 1 We understand the theory of op eration and know the diagnostic target 2 Use the functional diagram as a guide and map for testing based on the flow of information within the system 3 Consult the detailed information of a diagram to identify the exact test point 4 Go to the test point on the vehicle and gather data 5 Plug the data into your under standing of the system which is graphically displayed in the function al diagram 6 Repeat until done Conclusion Let s go back to the turn the key and nothing happens example page 38 but this time from the point of view of the expert instead of the learner The expert has already mastered the understanding of the parts and pieces of the system H e understands how the parts work together to carry out the sys tem processes There s already a func tional layout of the system in his mind H e doesn t have to follow the flow of information from the start if he doesn t want to He can literally test any point in the system and still Know where he is within the system processes H e under stands the implication of the test results H e can quickly isolate the problem M ost of us alread
10. eads Here s a brief outline of how we put the pieces together We gather data then give it meaning by relating it to the system and other data eN ext we gather enough additional data to fill in the blanks eAt some point we have enough data to understand how the system works N ow let s focus on some details techniques and be haviors for accomplishing this Thinking In Relationships Beyond comparing specs to a spec chart the value of test data is determined by our ability to relate it to what we want to accomplish E ven ad vanced waveform analysis is simply the practice of making finer and more detailed rela tionships So it seems that to get the most from our diag nostic experiences it s advis able to be in a heightened state of awareness A good place to start is to put the word relationships at the forefront of your diag nostic thoughts Then build on this by training yourself to ask active questions that will help guide you such as What can relate this to How does this re late Can relate this to that H ere are some practical examples eH ow does the current in a circuit relate to the buildup of a coil s mag netic field eH ow does the 5 volt frequency sig nal that s peaking only to 4 1 volts relate to the performance of the engine and the scan data eHow does this bent VRS sensor wheel relate to the waveform eH ow does the block learn on a GM vehicle relate to the oxygen and
11. ss turned out to be the one easi est to overcome the ability to operate them H ere are a few tips for getting start ed Set up your workspace so your tools are accessible and convenient to use If they re not you re less likely to get them out when under time pressure This is especially important for laptop based tools You don t want to make a job more stressful because you haven t figured out how to fit the tools into an active workspace M aster the buttonology ASAP It s hard to focus on a tough job when you re trying to figure out what feature you need Fig 1 36 MOTOR May 2013 to access and what button to hit to get it M aster the features too Do you know your test equipment s capabili ties The tool is there to give you diag nostic power make sure you re getting the most out of it by understanding its features and options A key to getting over these challenges is getting your tools out before you need them In fact until you re comfortable with them get them out and use them every chance you get D uring the learning process espe cially with a lab scope you ll see mostly known good waveforms These are essential parts of your waveform analy sis foundation When you go to classes or read a case study keep an eye out for the new diag nostic tools and learn how their features are being used Reading the Data What do we do with the scan and waveform data once it s in our h
12. y understand the operation of a basic starter system If you do too does the above description apply to you also If so perhaps you know what it is to be an expert on a particular system You also know the rewards of true understanding which are efficiency and effectiveness It also means this article is about something you already do naturally Mi This article can be found online at www motormagazine com
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