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 connector.
  • The electric generating capacity of the alternator connector terminal 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. Perform voltage measurement at alternator connector

  • Disconnect connector, and measure at harness side.
  • Ignition switch: "ON"
  • Voltage between terminal engine-ECU ALTL line and body earth.
OK: System voltage

Q. Is the check result normal?
Go to Step 5.
Go to Step 3.

STEP 3. Check harness between engine-ECU connector terminal ALTL and alternator connector terminal.

  • Check power supply line for open/short circuit.

Q. Is the check result normal?
Go to Step 4.
Repair or replace the connector, or repair the damaged harness wire.

STEP 4. 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 5. Check harness between engine-ECU connector terminal ALTL and alternator connector terminal.

  • Check power supply line for damage.

Q. Is the check result normal?
Go to Step 6.
Repair or replace the connector, or repair the damaged harness wire.

STEP 6. 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 body earth.
OK: System voltage

Q. Is the check result normal?
Go to Step 7.
Replace the alternator.

STEP 7. Check harness between engine-ECU connector terminal ALTG and alternator connector terminal.

  • Check output line for short circuit.

Q. Is the check result normal?
Go to Step 8.
Repair or replace the connector, or repair the damaged harness wire.

STEP 8. Perform voltage measurement at 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: P range
  • Cooling fan: Not operated
  • Voltage between terminal ALTG and body 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 4.