Inspection Procedure 17: Engine-ECU Battery Back-up System

OPERATION

Backup power source is directly supplied to an engine-ECU connector terminal BACK from a battery.

PROBABLE CAUSES

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

DIAGNOSIS PROCEDURE

STEP 1. Check battery.

Check battery (Refer to GROUP 54A - Battery - On-vehicle Service - Battery test ).

Q. Is the check result normal?

	Go to Step 2.

	Replace the battery.

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 engine-ECU connector terminal BACK and battery. 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. Check the trouble symptoms.

Q. Does the trouble symptom persist?

	Replace the engine-ECU.

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