Inspection Procedure 18: Battery Run Down








OPERATION



  • The exciting currents of the alternator field coil are input into the engine ECU (terminal No. 62) from the alternator (terminal No. 3).
  • The electric generating capacity of the alternator (terminal No. 1) is restricted according to the signal from the engine ECU (terminal No. 60).

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 in alternator L terminal circuit
  • Short circuit in alternator G terminal circuit
  • 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. Connector check: B-115 alternator connector

Q. Is the check result normal?
Go to Step 3 .
Repair or replace the connector.

STEP 3. Perform voltage measurement at B-115 alternator connector

  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 3 and earth.
OK: System voltage

Q. Is the check result normal?
Go to Step 5 .
Go to Step 4 .

STEP 4. Connector check: B-08 engine-ECU connector

Q. Is the check result normal?

    Check and repair harness between B-115 (terminal No. 3) alternator connector and B-08 (terminal No. 62) engine-ECU connector.

    • Check power supply line for open/short circuit.
Repair or replace the connector.

STEP 5. Perform voltage measurement at B-115 alternator G terminal connector.

  • Disconnect connector, and measure at harness side.
  • Connect special tool test harness (MB991658) to all terminals except the terminal No.1.
  • Ignition switch: ON
  • Voltage between terminal No. 1 and earth.
OK: System voltage

Q. Is the check result normal?
Go to Step 6 .
Replace the alternator.

STEP 6. Connector check: B-08 engine-ECU connector

Q. Is the check result normal?
Go to Step 7 .
Repair or replace the connector.

STEP 7. Check harness between B-115 (terminal No. 1) alternator connector and B-08 (terminal No. 60) engine-ECU connector.

  • Check output line for short circuit.

Q. Is the check result normal?
Go to Step 8 .
Repair the damaged harness wire.

STEP 8. Perform voltage measurement at B-08 engine-ECU connector.

  • Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB992110) to measure at connector for inspection.
  • Engine: Idle operation after warm-up
  • Transmission: Neutral <M/T> or P range <A/T>
  • Cooling fan: Not operated
  • Voltage between terminal No. 60 and earth.
OK: Voltage increases when the headlamps are extinguished→illuminated.

Q. Is the check result normal?
Go to Step 9 .
Check alternator.

STEP 9. 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 ).