35C-TCL/ASC-ECU POWER SUPPLY CIRCUIT SYSTEM

Inspection Procedure 13: 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 light, 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 diagnostic trouble code may be stored. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C - CAN Bus Line Diagnostic Flow ).
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. 25) for the solenoid valve. The solenoid valve is energized by the valve relay, which is incorporated in ASC-ECU.
ASC-ECU contains the power supply circuit (terminal No.6) 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 through multi-purpose fuse No.12.
ASC-ECU contains the power supply circuit (terminal No.1) for the pump motor. The pump motor is energized by the motor switch, which is incorporated in ASC-ECU.
When malfunction occurs in ASC-ECU power supply, the communication with scan tool becomes unavailable.

PROBABLE CAUSES

Damaged wiring harness and connectors
Malfunction of fuse or fusible link
Improper tightening of battery terminal
Improper tightening of grounding bolt
Battery failure
Charging system failed
ASC-ECU malfunction

DIAGNOSIS

STEP 1. Battery check

Refer to GROUP 54A - Battery Test

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 - On-vehicle Service/Output Current Test

Is the charging system in good condition?

Go to Step 3

Repair or replace the charging system component(s).

STEP 3. Connector check: A-03 ASC-ECU connector, C-127 intermediate connector and C-417 ETACS-ECU connector.

Is the check result normal?

Go to Step 4

Repair the damaged connector.

STEP 4. Voltage measurement at the A-03 ASC-ECU connector

(1) Disconnect the ASC-ECU connector, connect special tool test harness (MB991709) to the harness-side connector, and then measure the voltage at the special tool connector side.

note	Do not connect the special tool test harness (MB991709) to ASC-ECU.

(2) Measure the voltage between terminal No.25 and body ground.

OK: Approximately system voltage

Is the check result normal?

Go to Step 7

Go to Step 5

STEP 5. Fusible link check: Check the fusible link No.27.

Is the check result normal?

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ASC-ECU connector terminal No.25 and the fusible link No.27. Then go to Step 16

Go to Step 6

STEP 6. Resistance measurement at A-03 ASC-ECU connector

(1) Removal the fusible link No.27.

(2) Disconnect the ASC-ECU connector, connect special tool test harness (MB991709) to the harness-side connector, and then measure the resistance at the special tool connector side.

note	Do not connect the special tool test harness (MB991709) to ASC-ECU.

(3) Measure the resistance between the terminal No.25 and the body ground.

OK: No continuity

Is the check result normal?

Replace the fusible link No.27. Then go to Step 16

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ASC-ECU connector terminal No.25 and the fusible link No.27, and then replace the fusible link No.27. Then go to Step 16

STEP 7. Voltage measurement at the A-03 ASC-ECU connector

(1) Disconnect the ASC-ECU connector, connect special tool test harness (MB991709) to the harness-side connector, and then measure the voltage at the special tool connector side.

note	Do not connect the special tool test harness (MB991709) to ASC-ECU.

(2) Measure the voltage between terminal No.1 and body ground.

OK: Approximately system voltage

Is the check result normal?

Go to Step 10

Go to Step 8

STEP 8. Check the fusible link No.26.

Is the check result normal?

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ASC-ECU connector terminal No.1 and the fusible link No.26. Then go to Step 16

Go to Step 9

STEP 9. Resistance measurement at A-03 ASC-ECU connector

(1) Removal the fusible link No.26.

(2) Disconnect the ASC-ECU connector, connect special tool test harness (MB991709) to the harness-side connector, and then measure the resistance at the special tool connector side.

note	Do not connect the special tool test harness (MB991709) to ASC-ECU.

(3) Measure the resistance between the terminal No.1 and the body ground.

OK: No continuity

Is the check result normal?

Replace the fusible link No.26. Then go to Step 16

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ASC-ECU connector terminal No.1 and the fusible link No.26, and then replace the fusible link No.26. Then go to Step 16

STEP 10. Voltage measurement at the A-03 ASC-ECU connector

(1) Disconnect the ASC-ECU connector, connect special tool test harness (MB991709) to the harness-side connector, and then measure the voltage at the special tool connector side.

note	Do not connect the special tool test harness (MB991709) to ASC-ECU.

(2) Ignition switch: "ON" position.

(3) Measure the voltage between terminal No.6 and body ground.

OK: Approximately system voltage

Is the check result normal?

Go to Step 14

Go to Step 11

STEP 11. Check the fuse No.12.

Visually check for open circuit in fuse No.12.

Is the check result normal?

Go to Step 12

Go to Step 13

STEP 12. Resistance measurement at A-03 ASC-ECU connector

(1) Disconnect the C-417 ETACS-ECU connector.

(2) Disconnect the A-03 ASC-ECU connector, connect special tool test harness (MB991709) to the harness-side connector, and then measure the resistance at the special tool connector side.

note	Do not connect the special tool test harness (MB991709) to ASC-ECU.

(3) Measure the resistance between the A-03 ASC-ECU connector terminal No.6 and the C-417 ETACS-ECU connector terminal No.5.

OK: Continuity exists (2 Ω or less)

Is the check result normal?

The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/How to Cope with Intermittent Malfunctions

The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ASC-ECU connector terminal No.6 and the C-417 ETACS-ECU connector terminal No.5. Then go to Step 16

STEP 13. Resistance measurement at A-03 ASC-ECU connector

(1) Disconnect the C-417 ETACS-ECU connector.

(2) Disconnect the ASC-ECU connector, connect special tool test harness (MB991709) to the harness-side connector, and then measure the resistance at the special tool connector side.

note	Do not connect the special tool test harness (MB991709) to ASC-ECU.

(3) Measure the resistance between the terminal No.8 and the body ground.

OK: No continuity

Is the check result normal?

Replace the fuse No.12. Then go to Step 16

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ASC-ECU connector terminal No.8 and the C-417 ETACS-ECU connector terminal No.5, and then replace the fuse No.12. Then go to Step 16

STEP 14. Resistance measurement at the A-03 ASC-ECU connector

(1) Disconnect the ASC-ECU connector, connect special tool test harness (MB991709) to the harness-side connector, and then measure the resistance at the special tool connector side.

note	Do not connect the special tool test harness (MB991709) to ASC-ECU.

(2) Measure the resistance between terminal No.13 and body ground, and between terminal No.38 and body ground.

OK: Continuity exists (2 Ω or less)

Is the check result normal?

Go to Step 15

An open circuit may be present in the ground circuit. Repair the wiring harness between the A-03 ASC-ECU connector terminal No.13 and the body ground, and between the A-03 ASC-ECU connector terminal No.38 and the body ground.

STEP 15. Retest the system.

Make sure that the scan tool cable is properly connected and the V.C.I. switch is "ON".

Is the communication with scan tool 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.

Is the communication with scan tool possible?

Return to Step 1

The procedure is complete.