Inspection Procedure 2: BMU power supply system




PROBABLE CAUSES



  • Open circuits of BMU power supply circuit, short circuits to earth or damage; poor contact of connector.
  • The BMU is failed.

DIAGNOSIS PROCEDURE


STEP 1. Check auxiliary battery



  • Check auxiliary battery (Refer to GROUP 54A - Auxiliary Battery - On-vehicle Service - Battery Test ).

Q. Is the check result normal?

Go to Step 2.
Replace the auxiliary battery.

STEP 2. Perform voltage measurement at BMU connector (BAT terminal).



  • Disconnect the connector, and measure at the wiring harness side.
  • Check the voltage between the BMU connector (BAT terminal) and body earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 3.

    Repair BAT line between BMU connector and ETACS-ECU connector.

STEP 3. Perform voltage measurement at BMU connector (IGCT terminal).


(1)Disconnect the connector, and measure at the wiring harness side.
(2)Operate the electric motor switch without the brake pedal is depressed and turn ON the power supply mode of electric motor switch.
(3)Check the voltage between the BMU connector (IGCT terminal) and body earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 4.
Repair IGCT line between BMU connector and IGCT control relay connector.

STEP 4. Check of damage in BAT line between auxiliary battery connector and BMU connector.


Q. Is the check result normal?

Go to Step 5.
Repair the connector(s) or wiring harness.

STEP 5. Check of damage in IGCT line between IGCT control relay connector and BMU connector.


Q. Is the check result normal?

Go to Step 6.
Repair the connector(s) or wiring harness.

STEP 6. Perform resistance measurement at BMU connector (GND terminal).



  • Disconnect the connector, and measure at the wiring harness side.
  • Check the resistance between BMU connector (GND line) and body earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 7.
Repair GND line between BMU connector and body earth.

STEP 7. Check the trouble symptom.


Q. Does the trouble symptom persist?

Replace the BMU.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).