Inspection Procedure 17: Battery Run Down

OPERATION

The exciting currents of the alternator field coil are input into the engine-ECU connector terminal ALTL from the alternator.
The electric generating capacity of the alternator is restricted according to the signal from the engine-ECU connector terminal ALTG.

COMMENTS ON TROUBLE SYMPTOM

The failure could possibly be caused by the failed alternator, defective alternator control system and so on.

PROBABLE CAUSES

Failed battery
Open/short circuit or harness damage in alternator L terminal circuit
Short circuit in alternator G terminal
Failed alternator
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check battery.

Check battery (Refer to GROUP 54A - Battery - On-vehicle Service - Battery Test ).

Q. Is the check result normal?

	Go to Step 2.

	Replace the battery.

STEP 2. M.U.T.-III diagnosis code

Q. Is diagnosis code set?

	Inspection chart for diagnosis code (Refer to ).

	Go to Step 3.

STEP 3. Perform voltage measurement at alternator connector

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal engine-ECU ALTL line and earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 6.

	Go to Step 4.

STEP 4. Check of open circuit, and short circuit in ALTG line between engine-ECU connector and alternator connector.

Q. Is the check result normal?

	Go to Step 5.

	Repair the connector(s) or wiring harness.

STEP 5. Check the trouble symptom.

Q. Does the trouble symptom persist?

	Replace the engine-ECU.

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

STEP 6. Check of damage in ALTL line between engine-ECU connector and alternator connector.

Q. Is the check result normal?

	Go to Step 7.

	Repair the connector(s) or wiring harness.

STEP 7. Perform voltage measurement at alternator connector.

Disconnect connector, and measure at alternator side.
Connect special tool Test Harness (MB991658) to all terminals except the terminal engine-ECU ALTG line.
Ignition switch: ON
Voltage between terminal engine-ECU ALTG line and earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 8.

	Replace the alternator.

STEP 8. Check of short circuit in ALTG line between alternator connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 9.

	Repair the damaged harness wire.

STEP 9. Perform voltage measurement at engine-ECU connector.

Measure engine-ECU terminal voltage.
Engine: Idle operation after warm-up
Transmission: Neutral
Cooling fan: Not operated
Voltage between terminal ALTG and earth.

OK: The voltage increases when the headlamp switch and the rear window defogger switch are turned ON from OFF.

Q. Is the check result normal?

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

	Go to Step 5.