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Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK -- ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After performing diagnostic system check, go to next step.
  2. Using scan tool, check for DTCs. If DTCs P0107, P0601, P0602, P0604, P0606, P0607, P1220, P1221, P1271, P1514, P1621, P1631, P1635, P1639, P1680, P1681 or P1683 are set, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If DTCs are not set, go to next step.
  3. Monitor Ignition 1 Signal Voltage parameter with a scan tool. Is ignition 1 signal voltage parameter at battery voltage? If yes, go to next step. If no, go to step  10.
  4. Command fuel pump on with a scan tool. Does fuel pump turn on? If yes, go to next step. If no, go to FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
  5. Turn ignition off. Remove an ignition coil. Install Spark Tester (J-26792) to coil boot. Attempt to start engine. Does spark tester spark? If yes, go to next step. If no, diagnose electronic ignition system. Go to ELECTRONIC IGNITION SYSTEM .
  6. Turn ignition off. Disconnect fuel injector harness multi-way connector. Probe fuel injector control circuit, PCM side, with a test light connected to battery voltage. Crank engine. Does test light flash when cranking engine? If yes, go to next step. If no, diagnose fuel injector circuit. See FUEL INJECTOR CIRCUIT DIAGNOSIS under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
  7. Turn ignition off. Install Fuel Pressure Gauge (J-34730-1A). Turn ignition on, with engine off. Command fuel pump on with a scan tool. Is fuel pressure within 48-52 psi (334-375 kPa) while fuel pump is operating? If yes, go to next step. If no, go to FUEL SYSTEMS .
  8. Disconnect Crankshaft Position (CKP) sensor. CKP sensor is located on left rear of engine block. See Figure. Attempt to start engine. Does engine start and continue to run? If yes, go to step  11. If no, go to next step.
  9. Inspect for collapsed air intake duct, restricted air filter element, fouled spark plugs, engine mechanical problem or restricted exhaust system. Check if ECT sensor is NOT close to actual engine temperature. Compare MAP/BARO parameters to another vehicle. The parameters should be close in value. Check for TP sensor being stuck in range. Repair as necessary. After repairs, go to step  12.
  10. Repair ignition 1 signal voltage circuit for an open or a short to ground. Replace fuse, if necessary. After repairs, go to next step.
  11. Replace CKP sensor. After replacing sensor, go to next step. If no, go to step  2.
  12. 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.
  13. Allow engine to reach operating temperature. Observe DTC information 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 - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If no DTCs are set, system is okay.
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