Inspection Procedure 11: ASC-ECU power supply circuit system

caution

When the ASC-ECU power supply voltage becomes 9.7 ± 0.3 V or less, the ABS warning lamp, ASC warning lamp, and ASC OFF indicator lamp illuminate, and the ABS and TCL/ASC controls are prohibited.
If the battery terminal is not tightened properly, a dump surge may occur and the power supply voltage may become abnormally high for a short time.
If there is any problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ).
Whenever ECU is replaced, ensure that the CAN bus lines are normal.

OPERATION

ASC-ECU contains the power supply circuit (terminal No.25) for the solenoid valve. The solenoid valve is energised by the valve relay, which is incorporated in ASC-ECU.
ASC-ECU contains the power supply circuit (terminal No. 32) for ASC-ECU. When the electric motor switch is turned "ON", the voltage is applied to the relay incorporated in junction block to turn "ON" the relay, and the power is supplied from the multi-purpose fuse No. 15.
ASC-ECU contains the power supply circuit (terminal No.1) for the pump motor. The pump motor is energised by the motor switch, which is incorporated in ASC-ECU.
When malfunction occurs in ASC-ECU power supply, the communication with M.U.T.-III becomes unavailable.

PROBABLE CAUSES

Damaged wiring harness and connectors
Fuse and fusible link malfunction
Improper tightening of battery terminal
Improper tightening of earth bolt
Auxiliary battery failure
ASC-ECU malfunction

DIAGNOSIS PROCEDURE

STEP 1. Auxiliary battery check

Refer to GROUP 54A - Battery Test

Q. Is the battery in good condition?

	Go to Step 2.

	Charge or replace the auxiliary battery. Then go to Step 2.

STEP 2. Connector check: A-14 ASC-ECU connector, C-128 intermediate connector, B-302 junction block connector, B-306 junction block connector

Q. Is the check result normal?

	Go to Step 3.

	NO : Repair the damaged connector.

STEP 3. Fusible link check: Check the fusible link No.24.

Q. Is the check result normal?

	Go to Step 5.

	Go to Step 4.

STEP 4. Resistance measurement at A-14 ASC-ECU connector

(1)Removal the fusible link No.24.

(2)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ABS check harness (MB992335) to ASC-ECU.

(3)Measure the resistance between the terminal No.25 and the body earth.
OK: No continuity

Q. Is the check result normal?

Replace the fusible link No.24. Then go to Step 16.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-14 ASC-ECU connector terminal No.25 and the fusible link No.24, and then replace the fusible link No.24. Then go to Step 16.

STEP 5. Voltage measurement at the A-14 ASC-ECU connector

(1)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335) to the harness-side connector, and then measure the voltage at the special tool connector side.

note

Do not connect the special tool ABS check harness (MB992335) to ASC-ECU.

(2)Measure the voltage between terminal No.25 and body earth.
OK: Approximately system voltage

Q. Is the check result normal?

Go to Step 6.

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-14 ASC-ECU connector terminal No.25 and the fusible link No.24. Then go to Step 16.

STEP 6. Check the fusible link No.22.

Q. Is the check result normal?

	Go to Step 8.

	Go to Step 7.

STEP 7. Resistance measurement at A-14 ASC-ECU connector

(1)Removal the fusible link No.22.

(2)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ABS check harness (MB992335) to ASC-ECU.

(3)Measure the resistance between the terminal No.1 and the body earth.
OK: No continuity

Q. Is the check result normal?

Replace the fusible link No.22. Then go to Step 16.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-14 ASC-ECU connector terminal No.1 and the fusible link No.22, and then replace the fusible link No.22. Then go to Step 16.

STEP 8. Voltage measurement at the A-14 ASC-ECU connector

(1)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335) to the harness-side connector, and then measure the voltage at the special tool connector side.

note

Do not connect the special tool ABS check harness (MB992335) to ASC-ECU.

(2)Measure the voltage between terminal No.1 and body earth.
OK: Approximately system voltage

Q. Is the check result normal?

Go to Step 9.

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-14 ASC-ECU connector terminal No.1 and the fusible link No.22. Then go to Step 16.

STEP 9. Check the fuse No.15.

Visually check for open circuit in fuse No.15.

Q. Is the check result normal?

	Go to Step 11.

	Go to Step 10.

STEP 10. Resistance measurement at A-14 ASC-ECU connector

(1)Disconnect the B-306 junction block connector.

(2)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ABS check harness (MB992335) to ASC-ECU.

(3)Measure the resistance between the terminal No.32 and the body earth.
OK: No continuity

Q. Is the check result normal?

Replace the fuse No.15. Then go to Step 16.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-14 ASC-ECU connector terminal No.32 and the B-306 junction block connector terminal No.8, and then replace the fuse No.15. Then go to Step 16.

STEP 11. Resistance measurement at A-14 ASC-ECU connector

(1)Disconnect the B-306 junction block connector.

(2)Disconnect the A-14 ASC-ECU connector, connect special tool ABS check harness (MB992335) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ABS check harness (MB992335) to ASC-ECU.

(3)Measure the resistance between the A-14 ASC-ECU connector terminal No.32 and the B-306 junction block connector terminal No.8.
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

Go to Step 12.

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-14 ASC-ECU connector terminal No.32 and the B-306 junction block connector terminal No.8. Then go to Step 15.

STEP 12. Measure the voltage at the B-302 junction block connector.

(1)Measure by backprobing without disconnecting the connector.

(2)Turn the electric motor switch to the "ON" position.

(3)Measure the voltage between the terminal No.4 and the body earth.
OK: Battery voltage

Q. Is the check result normal?

	Go to Step 14.

	Go to Step 13.

STEP 13. Wiring harness check

Check the wiring harness between B-302 junction block connector and electric motor switch connector for any abnormality.

Q. Is the check result normal?

	Diagnose the electric motor switch (Refer to GROUP 54A Electric Motor Switch - Troubleshooting ).

	Repair the wiring harness. Then go to Step 15.

STEP 14. Resistance measurement at A-14 ASC-ECU connector

(1)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ABS check harness (MB992335) to ASC-ECU.

(2)Measure the resistance between the terminal No.13 and the body earth, and between the terminal No.38 and the body earth.
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

Go to Step 15.

An open circuit may be present in the earth circuit. Repair the wiring harness between the A-14 ASC-ECU connector terminal No.13 and the body earth, and between the A-14 ASC-ECU connector terminal No.38 and the body earth.

STEP 15. Retest the system.

Q. Is the communication with M.U.T.-III possible?

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

	Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ). Then go to Step 16.

STEP 16. Retest the system.

Q. Is the communication with M.U.T.-III possible?

	This diagnosis is complete.

	Return to Step 1.