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 115 (ENGINE CONTROLS SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P1374: 3X REFERENCE CIRCUITDIAGNOSTIC 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 Pontiac Montana, 2002 Oldsmobile Silhouette, and 2002 Chevrolet Venture. 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 and run? If yes, go to next step. If no, go to step 4.
- Observe the Freeze Frame/Failure Records for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC or within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.
- Turn OFF the ignition. Disconnect the 6-way ignition control module connector. Remove the injector fuse. Turn ON the ignition, with the engine OFF. Momentarily probe the low resolution engine speed signal circuit at the ignition module harness connector with a test lamp connected to battery voltage. Observe the Engine Speed parameter with a scan tool. Is an Engine Speed displayed? If yes, go to step 8. If no, go to next step.
- Did the test lamp illuminate? If yes, go to step 7. If no, go to next step.
- Turn OFF the ignition. Disconnect the PCM. Turn ON the ignition, with the engine OFF. Test the low resolution engine speed signal circuit of the ignition control module for an open or a short to voltage. Did you find and correct the condition? If yes, go to step 12. If no, go to step 9.
- Turn OFF the ignition. Disconnect the PCM. Test the low resolution engine speed signal circuit of the ignition control module for a short to ground. Did you find and correct the condition? If yes, go to step 12. If no, go to step 9.
- Test for an intermittent and for a poor connection at the ignition control module. Did you find and correct the condition? If yes, go to step 12. If no, go to step 10.
- Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 12. If no, go to step 11.
- Replace the ignition control module. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step 12.
- Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN 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.