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 92 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 6.6L DIESEL)DIAGNOSTIC TESTSDTC P0612: FUEL INJECTION CONTROL MODULE INTERNAL FAULTDIAGNOSTIC 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 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. 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, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM.
- Attempt to start the engine. Does the engine start? If yes, see DIAGNOSTIC AIDS . If no, go to next step.
- Turn OFF the ignition. Remove the ignition 1 relay using J 43244 Relay Puller Pliers. Disconnect the ECM connector containing the ignition 1 relay control circuit. Turn ON the ignition. Probe the ignition 1 relay control circuit with a test lamp connected to a good ground. Does the test lamp illuminate? If yes, go to step 5. If no, go to next step.
- Using a Digital Multimeter (DMM), measure the resistance of the coil circuit of the ignition 1 relay. Does the resistance measure 60-80 ohms? If yes, go to step 7. If no, go to step 6.
- Repair the short to battery or ignition voltage on the ignition 1 relay control circuit. After repairs, go to step 8.
- Replace the ignition 1 relay. After repairs, go to step 8.
- Replace the ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram ECM. See ENGINE CONTROL MODULE under PROGRAMMING. After repairs, go to next step.
- Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2.
- Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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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.