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Diagnostic Procedures

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  1. Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. After performing diagnostic system check, go to next step.
  2. Crank engine for 15 seconds. Does scan tool display any DTCs that failed this ignition? If yes, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. If DTCs are not set, go to next step.
  3. Does scan tool display any Body Control Module (BCM) or Vehicle Theft Deterrent (VTD) DTCs? If yes, diagnose affected DTCs. See appropriate BODY CONTROL MODULES or ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If no, go to next step.
  4. Observe engine speed parameter with scan tool, while cranking engine. Is engine RPM indicated on scan tool? If yes, go to next step. If no, diagnose ignition system. Go to ELECTRONIC IGNITION SYSTEM  under IGNITION SYSTEMS.
  5. Turn ignition on, with engine off. Probe both sides of PCM 1 fuse located in underhood fuse/relay block with a test light connected to a good ground. Does test light illuminate on at least on side of fuse? If yes, go to next step. If no, go to IGNITION RELAY under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
  6. Monitor ignition 1 signal parameter with a scan tool. Is ignition 1 signal parameter at battery voltage? If yes, go to next step. If no, go to step  10 .
  7. Command fuel pump ON with a scan tool. Does fuel pump operate? If yes, go to next step. If no, go to FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
  8. Turn ignition off. Install fuel pressure gauge. The fuel pump operates for about 2 seconds when ignition is turned on. Fuel pressure must be observed when fuel pump is operating. Turn ignition on, with engine off. Observe fuel pressure while fuel pump is operating. Is fuel pressure within 55-62 psi (385-425 kPa)? If yes, go to next step. If no, go to FUEL SYSTEM PRESSURE TEST  in FUEL SYSTEMS.
  9. Check if ECT sensor is close to actual engine temperature. Check duct work between MAF sensor and throttle body for air leaks. Check for restricted exhaust system. Check for a malfunctioning MAF sensor, causing a no-start or a stall after a start condition. If you suspect this, disconnect MAF sensor. PCM will default to speed density in order to calculate engine load and intake air flow. If disconnecting MAF sensor corrects condition and connections are okay, MAF sensor is faulty. If disconnecting MAF sensor does not correct the condition, check for fouled spark plugs or for an engine mechanical problem. Compare MAP/BARO parameters to another vehicle. Parameter values should be close to each other. Repair as necessary. After repairs, go to step  11 .
  10. Test ignition 1 voltage circuits that are supplied by PCM 1 fuse for an open or for a short to ground. Replace fuse, if necessary. Did you find and correct condition? If yes, go to step  13 . If no, go to next step.
  11. Inspect for poor connections at harness connector of PCM. Did you find and correct condition? If yes, go to step  13 . If no, go to next step.
  12. Replace PCM. See appropriate REMOVAL & INSTALLATION article. After replacing PCM, go to next step.
  13. Clear DTCs with a scan tool. Turn ignition off for 30 seconds. Attempt to start engine. Does engine start and continue to run? If yes, go to next step. If no, go to step  2 .
  14. Warm engine to normal operating temperature. Observe Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. If no DTCs are set, system okay.
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