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 522 (CHARGING SYSTEM)DIAGNOSTIC TESTSDTC P0512: PCM DETECTS AN IMPROPER CRANK REQUEST INPUTDIAGNOSTIC PROCEDURE
2003 Chevrolet TrailBlazer 4.2 S, 4WD
Diagnostic Procedure
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedure
WARNING: This page is about a different car, the 2003 Oldsmobile Aurora and 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
- If engine electrical diagnostic system check was performed, go to next step. If engine electrical diagnostic system check was not performed, go to ENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECK under ON-VEHICLE TESTING.
- Connect scan tool to Data Link Connector (DLC). See COMPONENT LOCATIONS . Turn ON the ignition, with the engine OFF. With a scan tool, observe the CRANK REQUEST parameter in the PCM data list. The CRANK REQUEST parameter should display NO. If display is as specified, go to next step. If display is not as specified, go to step 4 .
- Turn ON the ignition, with the engine OFF. Turn the ignition to the START position. With a scan tool, observe the CRANK REQUEST parameter in the PCM data list. The CRANK REQUEST parameter should display YES. If display is as specified, problem is intermittent. Check wiring and connections. If display is not as specified, go to step 5 .
- Turn OFF the ignition. Disconnect the PCM connector C1. See COMPONENT LOCATIONS . Connect test light between the CRANK REQUEST circuit, PCM connector terminal No. 6 (Yellow wire) and ground. See WIRING DIAGRAMS . Turn ON the ignition, with the engine OFF. If the test light illuminates, go to step 6 . If the test light does not illuminate, go to step 9 .
- Turn OFF the ignition. Disconnect the PCM connector C1. See COMPONENT LOCATIONS . Connect test light between the CRANK REQUEST circuit, PCM connector terminal No. 6 (Yellow wire) and ground. See WIRING DIAGRAMS . Turn the ignition to the START position. If the test light illuminates, go to step 9 . If the test light does not illuminate, go to step 7 .
- Test the CRANK REQUEST circuit Yellow wire for a short to voltage. See WIRING DIAGRAMS . If problem exists, repair as necessary. After repair, go to step 12 . If problem does not exist, go to step 8 .
- Test the CRANK REQUEST circuit Yellow wire for a high resistance or open. If problem exists, repair as necessary. After repair, go to step 12 . If problem does not exist, go to next step.
- Inspect for poor connections at the ignition switch. See appropriate STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. If problem exists, repair as necessary. After repair, go to step 12 . If problem does not exist, go to step 10 .
- Inspect PCM harness connector for poor connections. If problem does not exist, go to step 11 . If problem exists, repair as necessary. After repair, go to step 12 .
- Replace the ignition switch. See appropriate REMOVAL & INSTALLATION article under STEERING COLUMN SWITCHES in ACCESSORIES & EQUIPMENT. If problem exists, repair as necessary. After repair, go to step 12 .
- Replace PCM. See REMOVAL & INSTALLATION article in ENGINE PERFORMANCE. Program PCM. After repair, go to next step.
- Using scan tool, clear DTCs. Start engine. If DTC P0512 does not reset, system is okay. If DTC P0512 resets, go to step 2 and retest.
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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.