Inspection Procedure 17: 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 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. Connector check: B-117 alternator connector

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

STEP 3. Perform voltage measurement at B-117 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 7 .
Go to Step 4 .

STEP 4. Connector check: B-26 engine-ECU connector

Q. Is the check result normal?
Go to Step 5 .
Repair or replace the connector.

STEP 5. Check harness between B-26 (terminal No. 62) engine-ECU connector and B-117 (terminal No. 3) alternator connector.

  • Check power supply line for open/short circuit.

Q. Is the check result normal?
Go to Step 6 .
Repair the damaged harness wire.

STEP 6. 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 7. Check harness between B-26 (terminal No. 62) engine-ECU connector and B-117 (terminal No. 3) alternator connector.

  • Check power supply line for damage.

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

STEP 8. Perform voltage measurement at B-117 alternator connector.

  • Disconnect connector, and measure at alternator 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 9 .
Replace the alternator.

STEP 9. Connector check: B-26 engine-ECU connector

Q. Is the check result normal?
Go to Step 10 .
Repair or replace the connector.

STEP 10. Check harness between B-117 (terminal No. 1) alternator connector and B-26 (terminal No. 60) engine-ECU connector.

  • Check output line for short circuit.

Q. Is the check result normal?
Go to Step 11 .
Repair the damaged harness wire.

STEP 11. Perform voltage measurement at B-26 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
  • Cooling fan: Not operated
  • Voltage between terminal No. 60 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 6