ASC
DTC C1073: Faulty motor drive circuit
CAUTION:
^ If there is any problem in the CAN bus lines, an incorrect diagnostic trouble code may be set. Prior to this diagnosis, diagnose the CAN bus lines.
^ 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.
OPERATION
^ 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.
^ The pump motor switch, which is incorporated in ASC-ECU, is always off unless the motor and solenoid valve check is activated when the vehicle is started.
^ ASC-ECU activates the pump motor by turning on the ECU built-in pump motor switch.
DTC SET CONDITIONS
If the pump motor switch voltage drop indicates high value when the pump motor operates or after the operation, the pump motor operation is stopped and this diagnostic trouble code is set.
PROBABLE CAUSES
Current trouble
^ Fusible link malfunction
^ Damaged wiring harness and connectors
^ Abnormality in battery or generator
^ ASC-ECU malfunction
Past trouble
^ Carry out diagnosis with particular emphasis on wiring harness and connector failures between the power supply circuit (A-02 ASC-ECU connector terminal No.1) to the ASC-ECU motor and the ground circuit (A-02 ASC-ECU connector terminal No.47). For diagnosis procedures, refer to How to treat past trouble.
DIAGNOSIS
Required Special Tools:
^ MB991958: Scan Tool (M.U.T.-III Sub Assembly)
^ MB991824: Vehicle Communication Interface (V.C.I.)
^ MB991827: M.U.T.-III USB Cable
^ MB991910: M.U.T.-III Main Harness
^ MB991997: ASC check harness
STEP 1. M.U.T.-III CAN bus diagnostics
Use scan tool to diagnose the CAN bus lines.
Q: Is the check result normal?
YES: Go to Step 3.
NO: Repair the CAN bus lines. On completion, go to Step 2.
STEP 2. Check whether the diagnostic trouble code is reset.
Q: Is DTC C1073 set?
YES: Go to Step 3.
NO: The procedure is complete.
STEP 3. Fusible link check: Check the fusible link No.26.
Q: Is the check result normal?
YES: Go to Step
5.
NO: Go to Step 4.
STEP 4. Resistance measurement at A-02 ASC-ECU connector
1) Removal the fusible link No.26.
2) Disconnect the connector, connect special tool MB991997 to the harness-side connector, and measure the resistance at the special tool connector side.
NOTE: Do not connect the special tool MB991997 to ASC-ECU.
3) Resistance between the terminal No.1 and the body ground.
OK: No continuity
Q: Is the check result normal?
YES: Replace the fusible link No.26.
NO: Repair the harness between the fusible link No.26 and A-02 ASC-ECU connector terminal No.1. Then replace the fusible link No.26.
STEP 5. Battery check
Refer to Battery Test.
Q: Is the battery in good condition?
YES: Go to Step 6.
NO: Charge or replace the battery.
STEP 6. Charging system check
Refer to Output Current.
Q: Is the charging system in good condition?
YES: Go to Step 7.
NO: Repair or replace the charging system component(s).
STEP 7. Voltage measurement at the A-02 ASC-ECU connector
1) Disconnect the connector, connect special tool MB991997 to the harness-side connector, and measure the voltage at the special tool connector side.
NOTE: Do not connect the special tool MB991997 to ASC-ECU.
2) Measure the voltage between the terminal No.1 and the body ground.
OK: Approximately battery voltage
Q: Is the check result normal?
YES: Go to Step 9.
NO: Go to Step 8.
STEP 8. Connector check: A-02 ASC-ECU connector
Q: Is the check result normal?
YES: The open circuit may be present in the solenoid valve power supply circuit. Repair the wiring harness between the A-02 ASC-ECU connector terminal No.1 and the fusible link No.26.
NO: Repair the defective connector.
STEP 9. Resistance measurement at A-02 ASC-ECU connector
1) Disconnect the connector, connect special tool MB991997 to the harness-side connector, and measure the resistance at the special tool connector side.
NOTE: Do not connect the special tool MB991997 to ASC-ECU.
2) Resistance between the terminal No.16 and body ground, and between the terminal No.47 and body ground.
OK: Continuity exists (2 ohms or less)
Q: Is the check result normal?
YES: Go to Step 11.
NO: Go to Step 10.
STEP 10. Connector check: A-02 ASC-ECU connector
Q: Is the check result normal?
YES: An open circuit may be present in the ground circuit. Repair the wiring harness between the A-02 ASC-ECU terminal No.16 and the body ground, and between the A-02 ASC-ECU terminal No.47 and the body ground.
NO: Repair the defective connector.
STEP 11. Check whether the diagnostic trouble code is reset.
1) Erase the diagnostic trouble code.
2) Drive the vehicle at 12 mph (20 km/h) or more.
NOTE: The ABS warning light does not turn OFF in some cases unless the vehicle runs at 12 mph (20 km/h) or higher.
Q: Is DTC C1073 set?
YES: Replace the ASC-ECU.
NO: Intermittent malfunction.