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 Procedures
- Install a scan tool. Does the scan tool turn ON? If yes, go to next step. If no, see SCAN TOOL DOES NOT POWER UP in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
- Turn ON the ignition, with the engine OFF. Attempt to establish communication with the listed control modules. If you are using a Tech 2, obtain the information using the Class 2 Message Monitor feature:
- PCM.
- Vehicle Theft Deterrent (VTD).
- Instrument Panel (IP) cluster.
- Electronic Brake Control Module (EBCM).
Does the scan tool communicate with all the listed control modules? If yes, go to next step. If no, see SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
- Attempt to start the engine. Does the engine start and idle? If yes, go to next step. If no, see ENGINE CRANKS BUT DOES NOT RUN in appropriate TROUBLE SHOOTING - NO CODES article.
- Select the DTC display function for the following control modules: PCM, VTD, IP Cluster and EBCM. Does the scan tool display any DTCs? If yes, go to next step. If no, go to step Β 9.
- With a scan tool, select Captured Info in order to store the powertrain DTC information. When complete, go to next step.
- Does the scan tool display DTCs which begin with a "U"? If yes, see appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If no, go to next step.
- Does the scan tool display DTC P0601 or P0602? If yes, see DTC P0601-P0607, P1600, P1621, P1627, P1680, P1681 & P1683: PCM MEMORYΒ under DIAGNOSTIC TESTS. If no, go to next step.
- Does the scan tool display DTC P0560 or P0620? If yes, see appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS. If no, see DIAGNOSTIC TROUBLE CODE DEFINITIONSΒ .
- Is the customer's concern with the automatic transmission? If yes, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS. If no, go to next step.
- Is the customer's concern with Inspection and Maintenance (I/M) testing? If yes, see INSPECTION/MAINTENANCE SYSTEM CHECKΒ under INSPECTION/MAINTENANCE PROCEDURES.
- Review the following symptoms. Hard start, surges/chuggles, lack of power, sluggishness, sponginess, detonation/spark knock, hesitation, sag, stumble, cuts out, misses, poor fuel economy, poor fuel fill quality, rough, unstable, or incorrect idle and stalling, dieseling, run-on and backfire. See appropriate TROUBLE SHOOTING - NO CODES article. Did you find and correct the condition? If yes, system is okay. If no, see INTERMITTENT CONDITIONSΒ .
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.
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