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 218 (ENGINE CONTROL SYSTEM - SELF-DIAGNOSTICS)SYSTEM TESTSMIL INOPERATIVEDIAGNOSTIC PROCEDURES
2003 Chevrolet TrailBlazer 4.2 S, 4WD
Diagnostic Procedures
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
- Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS .
- Connect scan tool. Turn ignition switch to RUN position, engine OFF. Does scan tool display any engine data? If yes, go to next step. If no, go to SCAN TOOL DOES NOT COMMUNICATE WITH PCM in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
- Observe Instrument Panel Cluster (IPC) assembly operation. Do all other IPC functions operate normally? If yes, go to next step. If no, go to appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
- Turn ignition switch to OFF position. Disconnect PCM White 34-pin harness connector (with MIL control circuit). Turn ignition switch to RUN position, engine OFF. Probe MIL control circuit on harness side using a 3-amp fuse jumper wire to ground. Does MIL illuminate? If yes, go to step 9. If no, go to next step.
- Did the fuse in the jumper wire open? If yes, go to next step. If no, go to step 7.
- Repair short to voltage in MIL control circuit. After repair, go to step 10.
- Backprobe MIL control circuit at IPC assembly with a 3-amp fuse jumper wire to ground. Does the MIL illuminate? If yes, go to next step. If no, go to appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
- Repair open in the MIL control circuit. After repair, go to step 10.
- Replace PCM. After repair, go to next step.
- Turn ignition switch to RUN position, engine OFF. Is MIL illuminated? If yes, go to next step. If no, go to next step 2.
- Use scan tool to clear DTCs. Turn ignition OFF for 30 seconds. Start engine. Observe MIL operation. Is MIL illuminated? If yes, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM. If no, system is okay at this time.
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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.