Inspection Procedure 17: Battery Run Down








COMMENTS ON TROUBLE SYMPTOM



  • Failure is possibly caused by failed alternator or generator control system.

PROBABLE CAUSES



  • Failed battery
  • Short circuit in alternator G terminal
  • Failed alternator
  • Failed engine-ECU

DIAGNOSIS PROCEDURE


STEP 1. Check battery voltage.



  • Measure battery voltage at cranking.
OK: 8 V or more

Q. Is the check result normal?

Go to Step 2 .
Battery check (Refer to GROUP 54A - Battery - On-vehicle Service - Battery Test ).

STEP 2. Connector check: B-14 alternator connector


Q. Is the check result normal?

Go to Step 3 .
Repair or replace the connector.

STEP 3. Perform voltage measurement at B-14 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-29 engine-ECU connector


Q. Is the check result normal?


    Check and repair harness between B-14 (terminal No. 3) alternator connector and B-29 (terminal No. 62) engine-ECU connector.

    • Check power supply line for open/short circuit.
Repair the damaged harness wire.

STEP 5. Perform voltage measurement at B-14 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. Check harness between B-14 (terminal No. 1) alternator connector and B-29 (terminal No. 60) engine-ECU connector.



  • Check output line for open/short circuit.

Q. Is the check result normal?

Go to Step 7 .
Repair the damaged harness wire.

STEP 7. Perform voltage measurement at B-29 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: Voltage increases when the headlamps are extinguished→illuminated.

Q. Is the check result normal?

Go to Step 8 .

    Check alternator.

STEP 8. 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 ).