Code No. P1603: Battery Backup Circuit Malfunction

FUNCTION

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

TROUBLE JUDGEMENT

Check Conditions

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

Judgement Criterion

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

FAIL-SAFE AND BACKUP FUNCTION

All diagnosis codes are set once failure judgement 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. 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 diagnosis code P1603 set?

	Go to Step 3.

	Check end.

STEP 3. Voltage measurement at engine-ECU connector (BACK terminal).

(1)Disconnect the connector, and measure at the wiring harness side.

(2)Check the voltage between the engine-ECU connector (BACK terminal) and body earth.
OK: System voltage

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector(s), or check and repair the harness of short to earth and open circuit in BACK line between battery and engine-ECU connector.

STEP 4. Check of harness damage in BACK line between the battery and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 5.

	Repair the connector(s) or wiring harness.

STEP 5. 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 ).