INSPECTION PROCEDURE 2: ABS-ECU power supply system

<LH drive vehicles>

<RH drive vehicles>

OPERATION

The ABS-ECU is energized by the ignition switch (IG1) through multi-purpose fuse 2 and the ABS-ECU terminal 20.
If the power supply to the ABS-ECU has failed, M.U.T.-III will not be able to communicate with it.

PROBABLE CAUSES

Damaged wiring harness or connector
Defective battery
Charging system failed
Malfunction of the hydraulic unit (integrated with ABS-ECU)

DIAGNOSIS

STEP 1. Voltage measurement at ABS-ECU connector A-03.

(1)Disconnect the connector A-03, and connect special tool ABS Check Harness (MB991974) to the wiring harness-side connector.

note

Do not connect special tool ABS Check Harness (MB991974) to the ABS-ECU.

(2)Turn the ignition switch to the "ON" position.
(3)Measure the voltage between terminal 20 and earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 3.

Go to Step 2.

STEP 2. Check the following connectors.

ABS-ECU connector A-03
Junction block connectors C-202 and C-203
Joint connector (6) C-01 <LH drive vehicles>, Joint connector (7) C-33 <RH drive vehicles> and intermediate connector C-124
Ignition switch connector C-307

Check the connectors, for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is the check result normal?

An open or short circuit may be present in the power supply line to the ABS-ECU. Repair the wiring harness between ABS-ECU connector A-03 terminal 20 and ignition switch connector C-307 terminal 2. Go to Step 8.

Repair or replace the damaged component(s). Then go to Step 8.

STEP 3. Resistance measurement at ABS-ECU connector A-03.

(1)Disconnect the connector A-03, and connect special tool ABS Check Harness (MB991974) to the wiring harness-side connector.

note

Do not connect special tool ABS Check Harness (MB991974) to the ABS-ECU.

(2)Measure the resistance between terminal 26 and earth.
OK: 2 ohm or less

Q. Is the check result normal?

Go to Step 5.

Go to Step 4.

STEP 4. Check ABS-ECU connector A-03 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is the check result normal?

An open circuit may be present in the earth circuit. Repair the wiring harness between ABS-ECU connector A-03 terminals 26 and the body earth. Then go to Step 8.

Repair or replace the damaged component(s). Then go to Step 8.

STEP 5. Check the battery.

Check the battery (Refer to GROUP 54A, Battery test

Q. Is the check result normal?

	Go to Step 6.

	Charge or replace the battery. Then go to Step 8.

STEP 6. Check the charging system.

Check the charging system (Refer to GROUP 16, Charging system

Q. Is the check result normal?

	Go to Step 7.

	Repair or replace the charging system component(s).Then go to Step 8.

STEP 7. Retest the system.

Q. Can the ABS-ECU communicate with the M.U.T.-III?

	It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction .

	Replace the ABS-ECU. Then go to Step 8.

STEP 8. Retest the system.

Q. Can the ABS-ECU communicate with the M.U.T.-III?

	The procedure is complete.

	Go to Step 1.