Code No. P1603: Battery Backup Circuit Malfunction

OPERATION

Power is directly supplied to the engine-ECU connector terminal BACK from the battery.

FUNCTION

The engine-ECU checks open circuit in the battery backup line.

TROUBLE JUDGMENT

Check Conditions

Engine starting sequence was completed.
Battery positive voltage is more than 10 V.

Judgment Criterion

Battery backup line voltage is less than 6 V for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION

All diagnosis codes are stored once failure judgment is completed.

PROBABLE CAUSES

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

DIAGNOSIS PROCEDURE

STEP 1. 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 set?

	Go to Step 2.

	Check end.

STEP 2. Perform voltage measurement at engine-ECU connector.

Disconnect connector, and measure at harness side.
Voltage between terminal BACK and body earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 3.

	Repair or replace the connector, or check and repair harness between the battery and engine-ECU connector terminal BACK. Check power supply line for open/short circuit.

STEP 3. Check harness between the battery and engine-ECU connector terminal BACK.

Check power supply line for damage.

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 4. 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 ).