Code No. P1603: Battery Backup Circuit Malfunction








FUNCTION



  • The engine-ECU (terminal No. 104) checks open circuit in the battery backup line.

TROUBLE JUDGMENT


Check Conditions
  • Engine starting sequence was completed.
  • Battery positive voltage is 10 V or higher.
Judgment Criterion
  • Battery backup line voltage has continued to be 6 V or lower for 2 seconds.

PROBABLE CAUSES



  • Open/short circuit or harness damage in battery backup line circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE


STEP 1. Check the battery condition.


Q. Was the battery terminal removed just before reading the diagnosis code?

Go to Step 2 .
Go to Step 3 .

STEP 2. M.U.T.-III diagnosis code



  • Temporarily place the ignition switch in "LOCK" (OFF) position, and 10 seconds after that, place it in "ON" position again.

Q. Is the diagnosis code of P1603 output?

Go to Step 3 .
Check end.

STEP 3. Connector check: B-30 engine-ECU connector


Q. Is the check result normal?

Go to Step 4 .
Repair or replace the connector.

STEP 4. Perform voltage measurement at B-30 engine-ECU connector.



  • Disconnect connector, and measure at harness side.
  • Voltage between terminal No. 104 and earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 5 .

    Check and repair harness between the battery and B-30 (terminal No. 104) engine-ECU connector.

    • Check power supply line for open/short circuit.

STEP 5. Check harness between the battery and B-30 (terminal No. 104) engine-ECU connector.



  • Check power supply line for damage.

Q. Is the check result normal?

Go to Step 6 .
Repair the damaged harness wire.

STEP 6. M.U.T.-III diagnosis code



  • Reconfirmation of diagnosis code.

Q. Is diagnosis code set?

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