Inspection Procedure 12: 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 display, and ASC OFF display illuminate, and the ABS, stability control, and TCL 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 Diagnosis Table ).
Whenever ECU is replaced, ensure that the CAN bus lines are normal.
When the hydraulic unit (integrated with ASC-ECU) is replaced, always carry out the calibration of the steering wheel sensor, the G and yaw rate sensor and brake fluid pressure sensor (Refer to , and ).

OPERATION

ASC-ECU contains the power supply circuit (terminal No.32) 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.2) for ASC-ECU. The power is supplied from the fusible link No.34 <4A9, 4B1> or fusible link No.44 <BWC> through the multi-purpose fuse No.17.
ASC-ECU contains the power supply circuit (terminal No. 8) for ASC-ECU. When the ignition switch (IG1) is turned ON, the voltage is applied to the relay incorporated in ETACS-ECU to turn ON the relay, and the power is supplied from the fusible link No. 34 <4A9, 4B1> or fusible link No.44 <BWC> through multi-purpose fuse No. 12.
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
Battery failure
Charging system failed
ASC-ECU malfunction

DIAGNOSIS PROCEDURE

STEP 1. Battery check

Refer to GROUP 54A - Battery Test

Q. Is the battery in good condition?

	Go to Step 3.

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

STEP 2. Charging system check

Refer to GROUP 16 - Charging System

<4A9>,

<4B1>,

<BWC>,

<4B1-T/C>.

Q. Is the charging system in good condition?

	Go to Step 3.

	Repair or replace the charging system component(s).

STEP 3. Connector check: A-58 ASC-ECU connector, C-128 intermediate connector, C-212 ignition switch connector, C-309 ETACS-ECU connector, C-315 ETACS-ECU connector, C-317 ETACS-ECU connector

Q. Is the check result normal?

	Go to Step 4.

	NO : Repair the damaged connector.

STEP 4. Fusible link check: Check the fusible link No.27.

Q. Is the check result normal?

	Go to Step 6.

	Go to Step 5.

STEP 5. Resistance measurement at A-58 ASC-ECU connector

(1)Removal the fusible link No.27.

(2)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

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

Q. Is the check result normal?

Replace the fusible link No.27. Then go to Step 21.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-58 ASC-ECU connector terminal No.32 and the fusible link No.27, and then replace the fusible link No.27. Then go to Step 21.

STEP 6. Voltage measurement at the A-58 ASC-ECU connector

(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the voltage at the special tool connector side.

note

Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(2)Measure the voltage between terminal No.32 and body earth.
OK: Approximately battery voltage

Q. Is the check result normal?

Go to Step 7.

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-58 ASC-ECU connector terminal No.32 and the fusible link No.27. Then go to Step 21.

STEP 7. Check the fuse No.12.

Visually check for open circuit in fuse No.12.

Q. Is the check result normal?

	Go to Step 9.

	Go to Step 8.

STEP 8. Resistance measurement at A-58 ASC-ECU connector

(1)Disconnect the C-317 ETACS-ECU connector.

(2)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(3)Resistance between the terminal No.8 and the body earth.
OK: No continuity

Q. Is the check result normal?

Replace the fuse No.12. Then go to Step 21.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-58 ASC-ECU connector terminal No.8 and the C-317 ETACS-ECU connector terminal No.5, and then replace the fuse No.12. Then go to Step 21.

STEP 9. Check the fuse No.17.

Visually check for open circuit in fuse No.17.

Q. Is the check result normal?

	Go to Step 11.

	Go to Step 10.

STEP 10. Resistance measurement at A-58 ASC-ECU connector

(1)Disconnect the C-315 ETACS-ECU connector.

(2)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(3)Resistance between the terminal No.2 and the body earth.
OK: No continuity

Q. Is the check result normal?

Replace the fuse No.17. Then go to Step 21.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-58 ASC-ECU connector terminal No.2 and the C-315 ETACS-ECU connector terminal No.4, and then replace the fuse No.17. Then go to Step 21.

STEP 11. Measure the voltage at the C-309 ETACS-ECU connector.

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

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

Q. Is the check result normal?

	Go to Step 14.

	Go to Step 12.

STEP 12. Fusible link check: Check the fusible link No.34 <4A9, 4B1> or No.44 <BWC>.

Q. Is the check result normal?

	Go to Step 14.

	Go to Step 13.

STEP 13. Resistance measurement at C-309 ETACS-ECU connector

(1)Removal the fusible link No.34 <4A9, 4B1> or No.44 <BWC>.

(2)Disconnect the C-309 ETACS-ECU connector, and then measure the resistance at the connector side.

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

Q. Is the check result normal?

	Replace the fusible link No.34 <4A9, 4B1> or No.44 <BWC>. Then go to Step 21.

	The short circuit may be present in the power supply circuit. Repair the wiring harness between the C-309 ETACS-ECU connector terminal No.1 and the fusible link No.34 <4A9, 4B1> or No.44 <BWC>, and then replace the fusible link No.34 <4A9, 4B1> or No.44 <BWC>. Then go to Step 21.

STEP 14. Resistance measurement at fusible link No.34 <4A9, 4B1> or No.44 <BWC> and C-309 ETACS-ECU connector

(1)Disconnect the C-309 ETACS-ECU connector and fusible link No.34 <4A9, 4B1> or No.44 <BWC>, and then measure the resistance at the harness connector side.

(2)Resistance between the fusible link No.34 <4A9, 4B1> or No.44 <BWC> and C-309 ETACS-ECU connector terminal No.1.
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

	Go to Step 15.

	The open circuit may be present in the power supply circuit. Repair the wiring harness between the fusible link No.34 <4A9, 4B1> or No.44 <BWC> and C-309 ETACS-ECU connector terminal No.1. Then go to Step 21.

STEP 15. Resistance measurement at A-58 ASC-ECU connector

(1)Disconnect the C-317 ETACS-ECU connector.

(2)Disconnect the A-58 ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(3)Resistance between the A-58 ASC-ECU connector terminal No.8 and the C-317 ETACS-ECU connector terminal No.5.
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

Go to Step 16.

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-58 ASC-ECU connector terminal No.8 and the C-317 ETACS-ECU connector terminal No.5. Then go to Step 21.

STEP 16. Resistance measurement at A-58 ASC-ECU connector

(1)Disconnect the C-315 ETACS-ECU connector.

(2)Disconnect the A-58 ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(3)Resistance between the A-58 ASC-ECU connector terminal No.2 and the C-315 ETACS-ECU connector terminal No.4.
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

Go to Step 17.

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-58 ASC-ECU connector terminal No.2 and the C-315 ETACS-ECU connector terminal No.4. Then go to Step 21.

STEP 17. Measure the voltage at the C-317 ETACS-ECU connector.

(1)Measure by backprobing without disconnecting the connector.

(2)Turn the ignition switch to the ON position.

(3)Measure the voltage between the terminal No.6 and the body earth.
OK: Approximately battery voltage

Q. Is the check result normal?

	Go to Step 19.

	Go to Step 18.

STEP 18. Resistance measurement at C-317 ETACS-ECU connector and the C-212 ignition switch connector

(1)Disconnect the C-317 ETACS-ECU connector and C-212 ignition switch connector, and then measure the resistance at the harness connector side.

(2)Resistance between the C-317 ETACS-ECU connector terminal No.6 and C-212 ignition switch connector terminal No.2.
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

	Go to Step 19.

	The open circuit may be present in the power supply circuit. Repair the wiring harness between the C-317 ETACS-ECU connector terminal No.6 and C-212 ignition switch connector terminal No.2. Then go to Step 21.

STEP 19. Resistance measurement at A-58 ASC-ECU connector

(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.

note

Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.

(2)Resistance between the terminal No.16 and the body earth, and between the terminal No.47 and the body earth.
OK: Continuity exists (2 Ω or less)

Q. Is the check result normal?

Go to Step 20.

An open circuit may be present in the earth circuit. Repair the wiring harness between the A-58 ASC-ECU connector terminal No.16 and the body earth, and between the A-58 ASC-ECU connector terminal No.47 and the body earth.

STEP 20. Retest the system.

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

	Replace the hydraulic unit (ASC-ECU) (Refer to ). Then go to Step 21.

	Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction .)

STEP 21. Retest the system.

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

	Return to Step 1.

	This diagnosis is complete.