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. 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 3.

	Repair BACK line between battery and engine-ECU connector.

STEP 3. Check of damage in BACK line between battery and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 4.

	Repair the connector(s) or wiring harness.

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).