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 250 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING - 6.6L)FUEL SYSTEMSGLOW PLUG SYSTEM DIAGNOSISDIAGNOSTIC 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 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. 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 CONTROL under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO - DIESEL article. After performing Diagnostic System Check - Engine Controls, go to next step.
- Are DTCs P0117, P0118 or P0380 stored as history or current codes? If yes, diagnose affected DTC(s). See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO - DIESEL article. If no, go to next step.
- Turn ignition off. Disconnect all glow plugs. Using a test light connected to battery voltage, probe the spade terminal on each glow plug. If test light illuminates, go to next step. If test light does not illuminate, go to step 9 .
- Turn ignition on, with engine off. Ensure glow plugs are still disconnected. Probe each glow plug supply voltage circuit with test light connected to ground. Using scan tool, command glow plugs on. Does each circuit illuminate the test light? If yes, go to next step. If no, go to step 10 .
- Does test light illuminate all the time for each glow plug terminal, even when glow plugs are not commanded ON? If yes, go to next step. If no, go to step 11 .
- Disconnect glow plug supply voltage connection from the glow plug relay. Probe each glow plug terminal with a test light connected to ground. Does the test light illuminate for all terminals? If yes, go to next step. If no, go to step 8 .
- Repair short to voltage on glow plug supply voltage circuit. After repairs, go to step 11 .
- Replace glow plug relay/controller, located on upper intake manifold. After replacing glow plug relay/controller, go to step 11 .
- Replace all glow plugs that do not turn ON the test light. After replacing low plug(s), go to step 11 .
- Repair open in each circuit that does not turn ON the test light. After repairs, go next step.
- Operate vehicle within the conditions under which system fault was noted. Does the system operate properly? 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.