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 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 <M/T> or P range <CVT>
  • 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.