Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 143 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING)FUEL SYSTEM (DIESEL)IGNITION (GLOW PLUG) RELAY (6.6L)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.
- Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. After performing Diagnostic System Check - Engine Controls, go to next step.
- Turn OFF the ignition. Remove underhood electrical center cover. Remove IGN 1 relay with Relay Puller Pliers (J 43244). Probe IGN 1 relay 12-volt Switch Supply 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.
- Turn ON the ignition, with the engine OFF. Probe IGN 1 relay 12-volt Coil Supply 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.
- Probe Ignition 1 Relay Control circuit at underhood electrical center with test light connected to battery voltage. Does test light illuminate? If yes, go to next step. If no, go to step 10.
- Turn OFF the ignition. Jumper IGN 1 Relay Switch Supply circuit and IGN 1 Relay Load circuit together using fused jumper wire. Probe ECMRPV and INJR B fuses with test light connected to ground. Does test light illuminate for both fuses? If yes, go to next step. If no, go to step 13.
- Inspect for poor terminal contact at IGN relay underhood electrical center connector. Did you find and correct condition? If yes, go to step 14. If no, go to next step.
- Replace IGN 1 relay. After repairs, go to step 14.
- Repair open or short to ground in 12-volt switch supply to IGN 1 relay. After repairs, go to step 14.
- Repair open or short to ground in 12-volt Coil Supply circuit to IGN 1 relay. After repairs, go to step 14.
- Test IGN 1 Relay Control circuit for an open and repair as necessary. Did you find and correct the condition? If yes, go to step 14. If no, go to next step.
- Test for poor or intermittent connections at ECM and repair as necessary. Did you find and correct the condition? If yes, go to step 14. If no, go to next step.
- Replace ECM. Perform ECM relearn procedures. See PROGRAMMING in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO article. After repairs, go to step 14.
- Replace underhood electrical center. After repairs, go to next step.
- 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 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 - 6.6L 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.