Inspection Procedure 22

Inspection procedure 22: Generator output voltage is low (approximately 12.3 volts)














CIRCUIT OPERATION

- The ECM controls generator out put current by duty-controlling continuity between the generator G terminal (terminal No. 1) and ground.

TROUBLESHOOTING HINTS (The most likely causes for this charging system:)

- Charging system failed.

- Short circuit in harness between generator G terminal and ECM.

- ECM failed.

DIAGNOSIS

Required Special Tool:

- MB992110: Power Plant ECU Check Harness

STEP 1. Check harness connector B-108 at ECM for damage.

Q. Is the harness connector in good condition?

YES Go to Step 2.
NO Repair or replace it. Harness Connector Inspection.
Then confirm that the malfunction symptom is eliminated.
STEP 2. Measure the output voltage at ECM connector B-108 by using power plant ECU check harness special tool MB992110.





(1)Disconnect all ECM connectors. Connect the power plant ECU check harness special tool MB992110 between the separated connectors.
(2)Start the engine and run at idle.





(3)Measure the voltage between terminal No. 60 and ground.
NOTE:
Vehicles for Canada, the headlight, taillight, etc. remain lit even when the lighting switch is in "OFF" position but this is no problem for checks.

1. Engine: warming up, idling

2. Radiator fan: stopped

3. Headlight: OFF to ON

4. Stop light: OFF to ON

5. Rear defogger switch: OFF to ON

- Voltage should increase.
(4)Turn
the ignition switch to the "LOCK" (OFF) position.

Q. Did the measured voltage increase?

YES Go to Step 3.

NO Replace the generator. Then confirm that the malfunction symptom is eliminated.

STEP 3. Check harness connector B-15 at generator for damage.

Q. Is the harness connector in good condition?

YES Go to Step 4.
NO Repair or replace it. Harness Connector Inspection.
Then confirm that the malfunction symptom is eliminated.
STEP 4. Check for short circuit to ground between generator connector B-15 (terminal No. 1) and ECM connector B-108 (terminal No. 60).

Q. Is the harness wire in good condition?

YES Replace the ECM (Refer to Removal and Installation Removal and Replacement).
Then confirm that the malfunction symptom is eliminated.
NO Repair it. Then confirm that the malfunction symptom is eliminated.