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.
Diagnostic Procedure
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedure
WARNING: This page is about a different car, the 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
- Did you perform the Diagnostic System Check - Engine Controls (Alternative Fuels). If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS (ALTERNATIVE FUELS) under SELF-DIAGNOSTIC SYSTEM.
- Turn ignition switch to OFF position for 30 seconds. Start and idle the engine. Observe the DTC information using a scan tool. Did DTC P1020 fail this ignition cycle? If yes, go to step 4. If no, go to next step.
- Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING THE DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
- Idle the engine at normal operating temperature. Monitor the MISFIRE CURRENT COUNTERS using a scan tool. Are any of the misfire current counters incrementing? If yes, go to next step. If no, go step 7.
- Turn ignition switch to OFF position. Disconnect the AF fuel injector relay harness connector which displays the highest level of misfire. Probe the fuel injector control circuit from the PCM using a test light connected to battery voltage. With engine idling, observe the test light. Does the test light blink? If yes, go to step 15. If no, go to next step.
- Does the test light remain illuminated? If yes, go to step 14. If no, go to 13.
- Observe the DTC information using a scan tool. Are any of the DTCs P0201-P0204 also set? If yes, go to next step. If no, go to step 9.
- Turn ignition switch to OFF position. Disconnect the appropriate AF fuel injector relay harness connector. Probe the injector signal circuit, from the FICM, using a test light connected to a good ground. Turn ignition switch to RUN position, engine OFF. Does the test light illuminate? If yes, go to step 15. If no, go to step 12.
- Turn ignition switch to OFF position. Remove all of the AF injector relays from the mounting bracket. Command the AF enable relay ON and OFF using a scan tool. Feel for operation of each AF injector relay while commanding the AF enable relay ON and OFF. Isolate the inoperative relay. Did you complete the action? If yes, go to next step.
- Turn ignition switch to OFF position. Disconnect the harness connector of the isolated AF fuel injector relay. Turn ignition switch to RUN position, engine OFF. Probe the AF injector relay ignition voltage circuit using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 18.
- Probe the AF injector relay ground circuit using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step 15. If no, go to step 19.
- Check the fuel injector signal circuit for an open, or a short to ground between the FICM and the relay. If yes, go to step 23. If no, go to step 16.
- Check the fuel injector control circuit for an open or a short to voltage between the PCM and the relay. If yes, go to step 23. If no, go to step 16.
- Check the fuel injector control circuit for a short to ground between the PCM and the relay. If yes, go to step 23. If no, go to step 22.
- Check for an intermittent and for a poor connection at the AF injector relay. If yes, go to step 23. If no, go to step 20.
- Check for an intermittent and for a poor connection at the FICM. Did you find and correct the condition? If yes, go to step 23. If no, go to step 21.
- Check for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 23. If no, go to step 21.
- Repair the open or short to ground on the appropriate AF injector relay ignition voltage circuit. After repair, go to step 23.
- Repair the open on the appropriate ground circuit of the AF injector relay. After repair, go to step 23.
- Replace the AF injector relay. After repair, go to step 23.
- Replace the FICM. After repair, go to step 23.
- Replace the PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - CAVALIER & SUNFIRE article. Program PCM with correct vehicle software and calibration. After repair, go to next step.
- Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Turn ignition switch to RUN position, engine OFF. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING THE DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step 2. If no, go to next step.
- Observe the CAPTURE INFO using a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
RENDER: 1.0x
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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.