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.
Powertrain Diagnostic System Check
The powertrain diagnostic system check determines:
- If Malfunction Indicator Light (MIL) operates.
- If PCM is operating and can recognize a fault.
- If any DTCs are stored.
After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS and BASIC IGNITION SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. After performing necessary tests as described in the powertrain diagnostic system check, if no DTCs are indicated and driveability problems still exist, see appropriate TROUBLE SHOOTING - NO CODES article and SCAN TOOL USAGE .
- Connect scan tool to Data Link Connector (DLC). Turn ignition on, engine off. If scan tool powers up, go to next step. If scan tool does not power up, see SCAN TOOL DOES NOT POWER UP under appropriate BODY CONTROL MODULES article. Fig 1
- Turn ignition on, engine off. Attempt to establish communication with BCM, Sensing and Diagnostic Module (SDM), PCM and Electronic Brake/Traction Control Module (EBTCM). Record DTCs from each module if possible. If scan tool communicates with BCM, go to step 4. If scan tool does not communicate with BCM, go to next step.
- If scan tool communicates with SDM, see DTC U1064: LOST COMMUNICATIONS WITH BODY CONTROL MODULE in appropriate BODY CONTROL MODULES article. If scan tool does not communicate with SDM, see NO COMMUNICATION ON CLASS II DATA LINK in appropriate BODY CONTROL MODULES article.
- If DTCs are set in BCM, see DIAGNOSTIC TESTS in appropriate BODY CONTROL MODULES article. If no DTCs are set in BCM, go to next step.
- If DTCs are set in PCM, see DIAGNOSTIC TESTS . If no DTCs are set in PCM, go to next step.
- If DTCs are set in EBTCM, see DIAGNOSTIC TESTS in appropriate ANTI-LOCK/TCS article. If no DTCs are set in EBTCM, go to next step.
- Attempt to start engine. If engine does not start and run, see appropriate NO START - ENGINE CRANKS OK article in BASIC DIAGNOSTIC PROCEDURES - CARS EXCEPT METRO & PRIZM. If engine starts and runs, vehicle on-board diagnostics system is complete. Refer to scan tool data to determine if parameters are in correct operating range for system being diagnosed. Also, for symptom diagnostics, see TROUBLE SHOOTING - NO CODES in ENGINE PERFORMANCE.
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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.
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