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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 2 (ENGINE CONTROL SYSTEM - SELF-DIAGNOSTICS - 5.3L)SELF-DIAGNOSTIC SYSTEMPOWER MODE MISMATCHDIAGNOSTIC PROCEDURE
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Diagnostic Procedure

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedure
WARNING: This page is about a different variant/trim than selected.
NOTE: This procedure is used if the observed vehicle power mode does not match the actual ignition switch position. Open the driver's door and leave it open during this test. This will disable the RAP power mode and eliminate this power mode from the power mode parameter list.
  1. Connect a scan tool to Data Link Connector (DLC). Turn OFF the ignition. Using a scan tool, under the DIAGNOSTIC CIRCUIT CHECK menu, observe the CLASS 2 POWER MODE parameter. Does the displayed power mode parameter match the actual ignition switch position? If yes, go to next step. If no, go to step  6.
  2. Turn the ignition switch to the UNLOCK position. Using a scan tool, under the DIAGNOSTIC CIRCUIT CHECK menu, observe the CLASS 2 POWER MODE parameter. Does the displayed power mode parameter match the actual ignition switch position? If yes, go to next step. If no, go to step  6.
  3. Turn ON the ignition, with the engine OFF. Using a scan tool, under the DIAGNOSTIC CIRCUIT CHECK menu, observe the CLASS 2 POWER MODE parameter. Does the displayed power mode parameter match the actual ignition switch position? If yes, go to next step. If no, go to step  6.
    4. NOTE: The engine may start during this procedure. Turn the ignition OFF after verifying this power mode.
  4. Turn the ignition switch to the CRANK position. Using a scan tool, under the DIAGNOSTIC CIRCUIT CHECK menu, observe the CLASS 2 POWER MODE parameter. Does the displayed power mode parameter match the actual ignition switch position? If yes, go to next step. If no, go to step  6.
  5. Turn the ignition switch to the ACCY position. Using a scan tool, under the DIAGNOSTIC CIRCUIT CHECK menu, observe the CLASS 2 POWER MODE parameter. Does the displayed power mode parameter match the actual ignition switch position? If yes, see INTERMITTENT CONDITIONS . If no, go to next step.
    6. NOTE: The engine may start during this procedure. Turn the ignition OFF after verifying this power mode.
  6. Turn OFF the ignition. Disconnect the BCM. Hold the ignition switch in the position that indicated the incorrect power mode. Using a test light connected to a good ground, test the BCM ignition switch inputs for voltage. See BODY CONTROL MODULES in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Is voltage present on only the inputs specified for the ignition switch position? If yes, go to next step. If no, go to step  8.
    7. NOTE: The engine may start during this procedure. Turn the ignition OFF after verifying this power mode.
  7. Hold the ignition switch in the position that indicated the incorrect power mode. Using a test light connected to a good ground, test the BCM ignition switch inputs for voltage. See BODY CONTROL MODULES in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. If voltage does not exist on any inputs specified for the ignition switch position, go to step  9. If voltage exists on any inputs specified for the ignition switch position, go to step  11.
  8. Disconnect the ignition switch. See appropriate STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. Test the BCM ignition switch input circuits for a short to voltage. Test the BCM ignition switch circuits for a short between circuits. See BODY CONTROL MODULES in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Did you find and correct the condition? If yes, go to step  14. If no, go to step  10.
  9. Disconnect the ignition switch. See appropriate STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. Test the BCM ignition switch input circuits for an open. See BODY CONTROL MODULES in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Did you find and correct the condition? If yes, go to step  14. If no, go to next step.
  10. Inspect for poor connections and terminal tension at the harness connector of the ignition switch. Did you find and correct the condition? If yes, go to step  14. If no, go to step  12.
  11. Inspect for poor connections and terminal tension at the harness connector of the BCM. Did you find and correct the condition? If yes, go to step  14. If no, go to step  13.
  12. Replace the ignition switch. See appropriate STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. After ignition switch replacement, go to step  14.
    13. NOTE: After replacement of the BCM, perform the programming or set up procedure if required.
  13. Replace the BCM. See appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. After BCM replacement, go to next step.
    14. NOTE: The engine may start during this procedure. Turn the ignition OFF after verifying all power modes.
  14. Reconnect all disconnected components and connectors. Using a scan tool, under the DIAGNOSTIC CIRCUIT CHECK menu, observe the CLASS 2 POWER MODE parameter. Cycle the ignition switch through all possible positions, one at a time. Does the displayed power mode parameter match the actual ignition switch position? If yes, system is okay. If no, go to step  1.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.