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.
Engine Control Module (ECM) Diagnosis
To read and clear diagnostic trouble codes, use a Tech 2.
IMPORTANT: Use of a Tech 2 is recommended to clear diagnostic trouble codes from the ECM memory. Diagnostic trouble codes can also be cleared by turning the ignition "OFF" and disconnecting the battery power from the ECM for 30 seconds. Turning off the ignition and disconnecting the battery power from the ECM will cause all diagnostic information in the ECM memory to be cleared. Therefore, all the diagnostic tests will have to be re-run.
Since the ECM can have a failure which may affect only one circuit, following the diagnostic procedures in this section will determine which circuit has a problem and where it is.
If a diagnostic chart indicates that the ECM connections or the ECM is the cause of a problem, and the ECM is replaced, but this does not correct the problem, one of the following may be the reason:
- There is a problem with the ECM terminal connections. The terminals may have to be removed from the connector in order to check them properly.
- EEPROM program is not correct for the application. Incorrect components or reprogramming the ECM with the wrong EEPROM program may cause a malfunction and may or may not set a DTC.
- The problem is intermittent. This means that the problem is not present at the time the system is being checked. Make a careful physical inspection of all component and wiring associated with the affected system.
- There is a shorted solenoid, relay coil, or harness. Solenoids and relays are turned "ON" and "OFF" by the ECM using internal electronic switches called drivers. A shorted solenoid, relay coil, or harness will not damage the ECM but will cause the solenoid or relay to be inoperative.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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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