Inspection procedure 21: 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?

	Go to Step 2.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then confirm that the malfunction symptom is eliminated.

STEP 2. Measure the 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.

Engine: warming up, idling
Radiator fan: stopped
Headlight: OFF to ON
Stop light: OFF to ON
Rear defogger switch: OFF to ON

Voltage increases

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

Q. Is the measured voltage within the specified range?

Go to Step 3.

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?

	Go to Step 4.

	Repair or replace it. Refer to GROUP 00E, 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?

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, Diagnosis - ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> . Then confirm that the malfunction symptom is eliminated.

	Repair it. Then confirm that the malfunction symptom is eliminated.