Code No. P1A4C: BMU Control Power Supply Voltage Abnormal




TROUBLE JUDGEMENT


Check Condition
  • The power supply mode of the electric motor switch is ON, or the drive battery starts to be charged.
Judgement Criterion
  • The abnormal BMU control power supply voltage is detected.

FAIL-SAFE AND BACKUP FUNCTION



  • Not available

PROBABLE CAUSES



  • The auxiliary battery is failed.
  • When using the higher voltage from the outside of the vehicle than the voltage of the auxiliary battery
  • The installation of the auxiliary battery terminal is failed.
  • Open circuits of BMU control power supply circuit, short circuits to earth or damage; poor contact of connector
  • The BMU is failed.

DIAGNOSIS PROCEDURE


STEP 1. Auxiliary battery condition check


Q. Does the auxiliary battery start at the voltage higher than the voltage of the auxiliary battery from the outside of the vehicle recently?

Erase the diagnosis code, check end.
Go to Step 2.

STEP 2. Auxiliary battery condition check


Q. Is the installation status of the auxiliary battery terminal abnormal?

Repair.
Go to Step 3.

STEP 3. M.U.T.-III other system diagnosis code.


Q. Is the diagnosis code related to PHEV-ECU system stored?

Check PHEV-ECU system (Refer to ).
Go to Step 4.

STEP 4. 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 5.
Replace the auxiliary battery.

STEP 5. Perform voltage measurement at C-107 BMU connector


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

Q. Is the check result normal?

Go to Step 6.

    Repair BAT line between auxiliary battery and BMU connector.

STEP 6. 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 depressing the brake pedal 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 7.
Repair IGCT line between IGCT control relay connector and BMU connector

STEP 7. Check of damage in BAT line between auxiliary battery and BMU connector.


Q. Is the check result normal?

Go to Step 8.
Repair the connector(s) or wiring harness.

STEP 8. Check of damage in IGCT line between IGCT control relay connector and BMU connector.


Q. Is the check result normal?

Go to Step 9.
Repair the connector(s) or wiring harness.

STEP 9 M.U.T.-III diagnosis code.


Q. Is the diagnosis code stored?

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