Inspection Procedure 3

The Malfunction Indicator Lamp (SERVICE ENGINE SOON or Check Engine Lamp) Does Not Illuminate Right after the Ignition Switch Is Turned to the "ON" Position.

Malfunction Indicator Lamp (SERVICE ENGINE SOON Or Check Engine Lamp) Circuit Part 1:

Malfunction Indicator Lamp (SERVICE ENGINE SOON Or Check Engine Lamp) Circuit Part 2:

CIRCUIT OPERATION
- The malfunction indicator lamp (SERVICE ENGINE SOON or check engine lamp) power is supplied from the ignition switch.
- The ECM or the PCM controls the ground of the malfunction indicator lamp (SERVICE ENGINE SOON or check engine lamp) by turning the power transistor in the ECM or the PCM ON and OFF.

COMMENT
- The ECM or the PCM causes the malfunction indicator lamp (SERVICE ENGINE SOON or check engine lamp) to illuminate for 5 seconds immediately after the ignition switch is turned to the "ON" position occurred.

TROUBLESHOOTING HINTS (The most likely causes for this case:)
- Open malfunction indicator lamp (SERVICE ENGINE SOON or check engine lamp) circuit, harness damage or connector damage.
- Malfunction of the ECM or the PCM .

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A

STEP 1. Using scan tool MB991958, check data list item 16: Power Supply Voltage.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before. connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Set scan tool MB991958 to the data reading mode for item 16, Power Supply Voltage.
- Voltage should measure battery positive voltage.

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is battery positive voltage (approximately 12 volts) present?

YES: Go to Step 2.

NO: Refer to INSPECTION PROCEDURE 29 - Power Supply System and Ignition Switch - IG System.

STEP 2. Check harness connector C-04, C-05 at the combination meter for damage.

Q: Is the harness connector in good condition?

YES: Go to step 3.

NO: Repair or replace it. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.

STEP 3. Measure the power supply voltage at combination meter harness side connector C-04.

1. Disconnect the connector C-04 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.

3. Measure the voltage between terminal No. 42 and ground.
- Voltage should measure battery positive voltage.

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is battery positive voltage (approximately 12 volts) present?

YES: Go to Step 4.

NO: Check harness connectors C-203 and C-205 at intermediate connector for damage, and repair or replace as required. Refer to Harness Connector Inspection. If intermediate connectors are in good condition, repair harness wire between ignition switch connector C-303 (terminal No. 2) and combination meter connector C-04 (terminal No. 42) because of open circuit. Then confirm that the malfunction symptom is eliminated.

STEP 4. Check harness connector C-109 at ECM or PCM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 5.

NO: Repair or replace it. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.

STEP 5. Measure the power supply voltage at ECM or PCM connector C-109.

1. Disconnect the connector C-109 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.

3. Measure the voltage between terminal No. 7 and ground.
- Voltage should measure battery positive voltage.

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is battery positive voltage (approximately 12 volts) present?

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

NO: Check harness connector C-105 at intermediate connector for damage, and repair or replace as required. Refer to, Harness Connector Inspection. If intermediate connector is in good condition, repair harness wire between combination meter connector C-05 (terminal No. 14) and ECM or PCM connector C-109 (terminal No. 7) because of open circuit. Then confirm that the malfunction symptom is eliminated.