Inspection Procedure 4

The Service Engine Soon/Malfunction Indicator Lamp Remains Illuminated and Never Goes Out

Service Engine Soon/Malfunction Indicator Lamp Circuit:

Connectors:

CIRCUIT OPERATION
- The service engine soon/malfunction indicator lamp power is supplied from the ignition switch.
- The PCM controls the ground of the service engine soon/malfunction indicator lamp by turning the power transistor in the PCM ON and OFF.

COMMENT
- In cases such as the above, the cause is probably that the PCM is detecting a problem in a sensor or actuator, or that one of the malfunctions listed at right has probably occurred.

TROUBLESHOOTING HINTS (The most likely causes for this case:)
- Short-circuit between the service engine soon/malfunction indicator lamp and PCM.
- Malfunction of the PCM.

DIAGNOSIS

Required special tool:
- MB991502: Scan Tool (MUT-II)




STEP 1. Using scan tool MB991502, read the diagnostic trouble code (DTC).

CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991602.

1. Connect scan tool MB991502 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Read the DTC.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the DTC output?

YES: Refer to Diagnostic Trouble Code Chart.

NO: Go to Step 2.




STEP 2. Check the continuity at combination meter harness side connector C-04.

1. Disconnect the connector C-04 and measure at the harness side.
2. Check for the continuity between terminal 23 and ground.
- Should be open loop.

Q: Is the continuity normal?

YES: Replace the PCM. Then confirm that the malfunction symptom is eliminated.

NO: Check harness connector C-16 at the intermediate connector for damage, and repair or replace as required. Refer to Harness Connector Inspection. If intermediate connector C-16 is in good condition, repair a short circuit to ground between combination meter connector C-04 terminal 23 and PCM connector C-89 terminal 22. Then confirm that the malfunction symptom is eliminated.