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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 143 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING)IGNITION SYSTEMIGNITION RELAY DIAGNOSIS (4.3L)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 - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP , SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA or SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Turn OFF the ignition. Remove underhood electrical center cover. Remove IGN relay. Probe IGN relay battery positive voltage circuit at underhood electrical center terminal with test light connected to ground. Does test light illuminate? If yes, go to next step. If no, go to step  8.
  3. Turn ON the ignition, with the engine OFF. Probe IGN relay Ignition 1 voltage circuit at underhood electrical center with test light connected to ground. Does test light illuminate? If yes, go to next step. If no, go to step  9.
  4. Turn ON the ignition, with the engine OFF. Probe ignition main relay ground connector terminal with test light connected to 12 volts. Does test light illuminate? If yes, go to next step. If no, go to step  10.
  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, INJR A and INJR B fuses with test light connected to ground. Does test light illuminate for all fuses? If yes, go to next step. If no, go to step  10.
  6. Inspect for poor terminal contact at IGN relay underhood electrical center connector. Did you find and correct condition? If yes, go to step  11. If no, go to next step.
  7. Replace IGN relay. After repairs, go to step  11.
  8. Repair open or short to ground in battery positive voltage supply to IGN relay. After repairs, go to step  11.
  9. Repair Ignition 1 voltage circuit to IGN relay. After repairs, go to step  11.
  10. Replace underhood electrical center. After repairs, go to next step.
  11. Remove all test equipment except scan tool. Reconnect any disconnected components, fuses, etc. Turn ignition OFF for 30 seconds. Start engine and operate vehicle. Observe Malfunction Indicator Light (MIL), vehicle performance, and driveability. 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 - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP , SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA or SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO 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.