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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 143 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING)IGNITION SYSTEMIGNITION RELAY DIAGNOSIS (8.1L)DIAGNOSTIC PROCEDURE
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Diagnostic Procedure

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedure
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 2002 Saturn Vue, 2002 Pontiac Montana, 2002 Pontiac Aztek, 2002 Oldsmobile Silhouette, and 2002 Oldsmobile Bravada. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L "C", "G" & "K" SERIES TRUCKS article. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Turn OFF the ignition. Remove underhood fuse block cover. Remove ignition relay with Relay Puller Pliers (J 43244). Probe battery positive voltage circuit for ignition relay at underhood fuse block with test light connected to ground. Does test light illuminate? If yes, go to next step. if no, go to step  10.
  3. Turn ON the ignition, with the engine OFF. Probe Ignition 1 voltage circuit for ignition relay at underhood fuse block with test light connected to ground. Does test light illuminate? If yes, go to next step. If no, go to step  6.
  4. Turn ON the ignition, with the engine OFF. Probe coil ground circuit for ignition relay at underhood fuse block with test light connected to battery voltage. Does test light illuminate? If yes, go to next step. If no, go to step  7.
    5. NOTE: At least one test point of each fuse must illuminate test light.
  5. Turn OFF the ignition. Jumper IGN relay battery positive voltage circuit and IGN relay load circuit together using fused jumper wire. Probe ECM I, INJ A and INJ B fuses with test light connected to ground. Does test light illuminate for all fuses? If yes, go to step  8. If no, go to step  10.
  6. Turn OFF the ignition. Disconnect negative battery cable. Disconnect underhood fuse block electrical connectors. Test Ignition 1 voltage circuit of ignition relay at underhood fuse block electrical connector for an open circuit or for a short to ground. Did you find and correct the condition? If yes, go to step  11. If no, go to step  10.
  7. Turn OFF the ignition. Disconnect negative battery cable. Disconnect underhood fuse block electrical connectors. Test coil ground circuit of ignition relay at underhood fuse block electrical connector for a high resistance or for an open circuit. Did you find and correct the condition? If yes, go to step  11. If no, go to step  10.
  8. Inspect for poor terminal contact at ignition relay underhood electrical center connector. Did you find and correct condition? If yes, go to step  10. If no, go to next step.
  9. Replace ignition relay. After repairs, go to step  11.
    10. NOTE: DO NOT dissemble or attempt any repairs to underhood fuse block.
  10. Replace underhood electrical center. After repairs, go to next step.
  11. Clear DTCs with scan tool. Turn ignition OFF for 30 seconds. Start engine. Operate vehicle for 5 minutes. Does vehicle operate normally, with no MIL illumination and no stored DTCs? If yes, system is okay. If no, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 8.1L "C", "G" & "K" SERIES TRUCKS article.
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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.