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CHAPTER 1 The Diagnostic Process

CHAPTER 1 The Diagnostic Process. OBJECTIVES. After studying Chapter 1, the reader will be able to: Prepare for ASE computerized engine controls diagnosis (A8) certification test content area “E.” List the steps of the diagnostic process.

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CHAPTER 1 The Diagnostic Process

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  1. CHAPTER 1 The Diagnostic Process

  2. OBJECTIVES After studying Chapter 1, the reader will be able to: • Prepare for ASE computerized engine controls diagnosis (A8) certification test content area “E.” • List the steps of the diagnostic process. • Describe the simple preliminary tests that should be performed at the start of the diagnostic process. • List six items to check as part of a thorough visual inspection.

  3. OBJECTIVES • Explain the troubleshooting procedures to follow if a diagnostic trouble code has been set. • Explain the troubleshooting procedures to follow if no diagnostic trouble code has been set. • Discuss the type of scan tools that are used to assess vehicle components. • Describe the methods that can be used to reprogram (reflash) a vehicle computer.

  4. Data link connector (DLC) Drive cycle Flash code retrieval Key-on–engine off test (KOEO) Key-on–engine running test (KOER) Paper test Pending code Self-test automatic readout (STAR) Smoke machine Technical service bulletin (TSB) Trip KEY TERMS

  5. THE EIGHT-STEP DIAGNOSTIC PROCEDURE • It is important that all automotive service technicians know how to diagnose and troubleshoot engine computer systems. • The diagnostic process is a strategy that eliminates known-good components or systems in order to find the root cause of automotive engine performance problems. • All vehicle manufacturers recommend a diagnostic procedure, and the plan suggested in this chapter combines most of the features of these plans plus additional steps developed over years of real-world problem solving.

  6. THE EIGHT-STEP DIAGNOSTIC PROCEDURE • Verify the Problem (Concern) • Perform a Thorough Visual Inspection and Basic Tests • Check for obvious problems (basics, basics, basics). • Check everything that does and does not work. • Look for evidence of previous repairs. • Check oil level and condition. • Check coolant level and condition. • Use the paper test • Ensure adequate fuel level. • Check the battery voltage. • Check the spark using a spark tester. • Check the fuel pump pressure

  7. THE EIGHT-STEP DIAGNOSTIC PROCEDURE • Retrieve the Diagnostic Trouble Codes (DTCs) • Check for Technical Service Bulletins (TSBs) • Look Carefully at Scan Tool Data • Narrow the Problem to a System or Cylinder • Repair the Problem and Determine the Root Cause • Verify the Repair and Clear Any Stored DTCs

  8. FIGURE 1-1 A funnel is one way to visualize the diagnostic process. The purpose is to narrow the possible causes of a concern until the root cause is determined and corrected. FIGURE 1-2 Step #1 is to verify the customer concern or problem. If the problem cannot be verified, then the repair cannot be verified. THE EIGHT-STEP DIAGNOSTIC PROCEDURE

  9. “Original Equipment” Is Not a Four-Letter Word • To many service technicians, an original-equipment part is considered to be only marginal and to get the really “good stuff” an aftermarket (renewal market) part has to be purchased. However, many problems can be traced to the use of an aftermarket part that has failed early in its service life. Technicians who work at dealerships usually go immediately to an aftermarket part that is observed during a visual inspection. It has been their experience that simply replacing the aftermarket part with the factory originalequipment (OE) part often solves the problem.

  10. “Original Equipment” Is Not a Four-Letter Word • Original equipment parts are required to pass quality and durability standards and tests at a level not required of aftermarket parts. The technician should be aware that the presence of a new part does not necessarily mean that the part is good.

  11. FIGURE 1-3 A form that the customer should fill out if there is a driveablilty concern to help the service technician more quickly find the root cause. THE EIGHT-STEP DIAGNOSTIC PROCEDURE

  12. FIGURE 1-4 This is what was found when removing an air filter from a vehicle that had a lack-of-power concern. Obviously the nuts were deposited by squirrels or some other animal, blocking a lot of the airflow into the engine. THE EIGHT-STEP DIAGNOSTIC PROCEDURE

  13. Smoke Machine Testing • Vacuum (air) leaks can cause a variety of driveability problems and are often difficult to locate. One good method is to use a machine that generates a stream of smoke. Connecting the outlet of the smoke machine to the hose that was removed from the vacuum brake booster allows smoke to enter the intake manifold. Any vacuum leaks will be spotted by observing smoke coming out of the leak.

  14. FIGURE 1-5 Using a bright light makes seeing where the smoke is coming from easier. In this case, smoke was added to the intake manifold with the inlet blocked with a yellow plastic cap and smoke was seen escaping past a gasket at the idle air control. Smoke Machine Testing

  15. FIGURE 1-6 A spark tester connected to a spark plug wire or coil output. A typical spark tester will only fire if at least 25,000 volts is available from the coil, making a spark tester a very useful tool. Do not use one that just lights when a spark is present, because they do not require more than about 2,000 volts to light. THE EIGHT-STEP DIAGNOSTIC PROCEDURE

  16. FIGURE 1-7 Step #3 in the diagnostic process is to retrieve any stored diagnostic trouble codes. THE EIGHT-STEP DIAGNOSTIC PROCEDURE

  17. FIGURE 1-8 After checking for stored diagnostic trouble codes (DTCs), the wise technician checks service information for any technical service bulletins that may relate to the vehicle being serviced. THE EIGHT-STEP DIAGNOSTIC PROCEDURE

  18. FIGURE 1-10 Step #8 is very important. Be sure that the customer’s concern has been corrected. FIGURE 1-9 Looking carefully at the scan tool data is very helpful in locating the source of a problem. THE EIGHT-STEP DIAGNOSTIC PROCEDURE

  19. One Test Is Worth 1,000 “Expert” Opinions • Whenever any vehicle has an engine performance or driveability concern, certain people always say: • “Sounds like it’s a bad injector.” • “I’ll bet you it’s a bad computer.” • “I had a problem just like yours yesterday and it was a bad EGR valve.” • Regardless of the skills and talents of those people, it is still more accurate to perform tests on the vehicle than to rely on feelings or opinions of others who have not even seen the vehicle. Even your own opinion should not sway your thinking. Follow a plan, perform tests, and the test results will lead to the root cause.

  20. SCAN TOOLS • Scan tools are the workhorse for any diagnostic work on all vehicles. • Scan tools can be divided into two basic groups: • Factory scan tools. • Aftermarket scan tools

  21. FIGURE 1-12 Some scan tools use pocket PCs which make it very convenient to use. FIGURE 1-11 A TECH 2 scan tool is the factory scan tool used on General Motors vehicles. SCAN TOOLS

  22. RETRIEVAL OF DIAGNOSTIC INFORMATION • To retrieve diagnostic information from the PCM, use the following steps: • Locate and gain access to the data link connector (DLC). • Connect the scan tool to the DLC and establish communication. • Follow the on-screen instructions of the scan tool to correctly identify the vehicle. • Observe the scan data, as well as any diagnostic trouble codes. • Follow vehicle manufacturer’s instructions if any DTCs are stored. If no DTCs are stored, compare all sensor values with a factory acceptable range chart to see if any sensor values are out-of-range.

  23. TROUBLESHOOTING USING DIAGNOSTIC TROUBLE CODES • Pinning down causes of the actual problem can be accomplished by trying to set the opposite code. • For example, if a code indicates an open throttle position (TP) sensor (high resistance), clear the code and create a shorted (low-resistance) condition. • This can be accomplished by using a jumper wire and connecting the signal terminal to the 5-volt reference terminal.

  24. TROUBLESHOOTING USING DIAGNOSTIC TROUBLE CODES • Methods for Clearing Diagnostic Trouble Codes

  25. FLASH CODE RETRIEVAL ON OBD-I GENERAL MOTORS VEHICLES • The GM system uses a “check engine” or “check engine soon” MIL to notify the driver of possible system failure. Under the dash (on most GM vehicles) is a data link connector (DLC) previously called an assembly line communications link (ALCL) or assembly line diagnostic link (ALDL). • Most General Motors diagnostic trouble codes can be retrieved by using a metal tool and contacting terminals A and B of the 12-pin DLC

  26. FIGURE 1-13 To retrieve flash codes from an OBD-I General Motors vehicle, connect terminals A and B with the ignition on–engine off. The M terminal is used to retrieve data from the sensors to a scan tool. FLASH CODE RETRIEVAL ON OBD-I GENERAL MOTORS VEHICLES

  27. Do Not Lie to a Scan Tool! • Because computer calibration may vary from year to year, using the incorrect year for the vehicle while using a scan tool can cause the data retrieved to be incorrect or inaccurate.

  28. RETRIEVING FORD DIAGNOSTIC CODES • The best tool to use during troubleshooting of a Ford vehicle is a self-test automatic readout (STAR) tester, new generation STAR (NGS), WDS (Worldwide Diagnostic System), or another scan tool with Ford capabilities. • If a STAR tester or scan tool is not available, a needle (analog) type of voltmeter can be used for all OBD-I (prior to 1996) systems.

  29. FIGURE 1-14 A Ford OBD-I self-test connector. The location of this connector can vary with model and year of vehicle. RETRIEVING FORD DIAGNOSTIC CODES

  30. RETRIEVING FORD DIAGNOSTIC CODES • Key On–Engine Off Test (On-Demand Codes or Hard Faults) • Separator Pulse • Continuous Memory Codes (Soft Codes) • Key On–Engine Running (KOER) Test • Steering,Brake, and Overdrive Switch Test • Dynamic Response Check

  31. Put a Wire in the Attic and a Light in the Basement! • Retrieving DTCs from a Ford using low-cost test equipment is easier when you remember the following: “Put a wire in the attic and a light in the basement.” After warming the engine to operating temperature, perform these simple steps: • 1. Locate the data link connector (DLC) under the hood. Connect a jumper wire from the single-wire pigtail called the self-test input to terminal #2 at the top (attic) of the connector. • 2. To read DTCs, connect a standard 12-volt test light (not a self-powered continuity light) to the positive battery terminal and the lower (basement) terminal (#4) of the DLC. Turn the ignition to on (engine off). The DTCs will be displayed by means of the flashes of the test light. • To clear stored Ford DTCs, simply disconnect the jumper wire from the self-test input while the codes are being flashed. This interruption is the signal to the computer to clear any stored DTCs.

  32. FIGURE 1-15 To retrieve Ford DTCs using a test light and a jumper wire, turn the ignition switch on (engine off) and make the connections shown. The test light will blink out the diagnostic trouble codes. Put a Wire in the Attic and a Light in the Basement!

  33. FLASH CODE RETRIEVAL ON CHRYSLER VEHICLES • To put the computer into the self-diagnostic mode, the ignition switch must be turned on and off twice within a 5-second period (on-off-on-off-on). • The computer will flash a series of fault codes. • Older Chrysler brand products flash the “check engine” lamp on the dash.

  34. OBD-II DIAGNOSIS • Starting with the 1996 model year, all vehicles sold in the United States must use the same type of 16-pin data link connector (DLC) and must monitor emission-related components. • Retrieving OBD-II Codes

  35. FIGURE 1-16 A typical OBD-II data link connector (DLC). The location varies with make and model and may even be covered, but a tool is not needed to gain access. Check service information for the exact location if needed. OBD-II DIAGNOSIS

  36. OBD-II ACTIVE TESTS • OBD-II Drive Cycle • Types of OBD-II Codes • Type A Codes. • Type B Codes. • Type C and D Codes. • OBD-II Freeze-Frame • Diagnosing Intermittent Malfunctions

  37. SERVICE/FLASH PROGRAMMING • Remote Programming • Direct Programming • Off-Board Programming

  38. FIGURE 1-17 The first step in the reprogramming procedure is to determine the current software installed using a scan tool. Not all scan tools can be used. In most cases using the factory scan tool is needed for reprogramming unless the scan tool is equipped to handle reprogramming. SERVICE/FLASH PROGRAMMING

  39. FIGURE 1-18 Follow the on-screen instructions. SERVICE/FLASH PROGRAMMING

  40. FIGURE 1-19 An Internet connection is usually needed to perform updates although some vehicle manufacturers use CDs which are updated regularly at a cost to the shop. SERVICE/FLASH PROGRAMMING

  41. FIGURE 1-20 Connecting cables and a computer to perform offboard programming. SERVICE/FLASH PROGRAMMING

  42. J2534 REPROGRAMMING • Legislation has mandated that vehicle manufacturers meet the SAE J2534 standards for all emissions-related systems on all new vehicles starting with model year 2004. • This standard enables independent service repair operators to program or reprogram emissions-related ECMs from a wide variety of vehicle manufacturers with a single tool.

  43. FIGURE 1-21 The J2534 pass-through reprogramming system does not need a scan tool to reflash the PCM on most 2004 and newer vehicles. J2534 REPROGRAMMING

  44. FIGURE 1-22 A typical J2534 universal reprogrammer that uses the J2534 standards. J2534 REPROGRAMMING

  45. MANUFACTURER’S DIAGNOSTIC ROUTINES • Each vehicle manufacturer has established their own diagnostic routines and they should be followed. Most include the following steps: • Retrieve diagnostic trouble codes. • Check for all technical service bulletins that could be related to the stored DTC. • If there are multiple DTCs, the diagnostic routine may include checking different components or systems instead of when only one DTC was stored. • Perform system checks. • Perform a road test matching the parameters recorded in the freeze-frame to check that the repair has corrected the malfunction. • Repeat the road test to cause the MIL to be extinguished.

  46. COMPLETING SYSTEM REPAIRS • After the repair has been successfully completed, the vehicle should be driven under similar conditions that caused the original concern. • Verify that the problem has been corrected. • To perform this test drive, it is helpful to have a copy of the freezeframe parameters that were present when the DTC was set. • By driving under similar conditions, the PCM may perform a test of the system and automatically extinguish the MIL.

  47. PROCEDURES FOR RESETTING THE PCM • The PCM can be reset or cleared of previously set DTCs and freeze-frame data in the following ways: • Driving the Vehicle. • Clear DTCs Using a Scan Tool. • Battery Disconnect.

  48. The Brake Pedal Trick • If the vehicle manufacturer recommends that battery power be disconnected, first disconnect the negative battery cable and then depress the brake pedal. Because the brake lights are connected to battery power, depressing the brake pedal causes all of the capacitors in the electrical system and computer(s) to discharge through the brake lights.

  49. ROAD TEST (DRIVE TRACE) • Use the freeze-frame data and test-drive the vehicle so that the vehicle is driven to match the conditions displayed on the freezeframe. • If the battery has been disconnected, then the vehicle may have to be driven under conditions that allow the PCM to conduct monitor tests • Universal Drive Cycle

  50. Drive the Light Out • If working on a vehicle that is subject to state emission testing, it is best to not clear codes. When diagnostic trouble codes are cleared, all of the monitors have to be rerun and this can be a time consuming job. Instead of clearing the code, simply drive the vehicle until the PCM clears the code. This will likely take less time compared to trying to drive the vehicle under varying conditions to run all of the monitors.

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