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.
Circuit Description
The Diagnostic System Check - Engine Controls must be the starting point for any driveability complaint diagnosis. Perform a careful inspection of the Powertrain Control Module (PCM) and engine grounds for being clean and tight. Diagnostic System Check - Engine Controls is an organized approach to identifying a problem created by an electronic engine control system malfunction.
The PCM controls the Malfunction Indicator Light (MIL) by providing a ground path through the MIL control circuit to turn ON the MIL. When the ignition is turned ON, the MIL will remain on until the engine is running, if no DTC are stored. If MIL is illuminated, then the engine stalls, MIL will remain illuminated so long as the ignition is ON.
Perform the Engine Controls Diagnostic System Check, when the following conditions are present:
- When the MIL does not turn ON when the ignition switch is turned to the RUN position. See above for MIL operation.
- When the MIL remains ON while the engine is running.
- When the MIL is flashing while the engine is running.
- When a driveability symptom is determined.
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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.