C1073

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 the ECU is replaced, ensure that the CAN bus lines are normal.
^ When the hydraulic unit (integrated with ASC-ECU) is replaced, always perform the calibration of steering wheel sensor, G and yaw rate sensor, brake fluid pressure sensor, cut valve, and inlet valve.

CIRCUIT OPERATION
^ ASC-ECU contains the power supply circuit (terminal No. 1) for the motor. The pump motor is energized by the pump motor switch, which is incorporated in ASC-ECU.
^ The pump motor switch in ASC-ECU is turned off at all times unless during the motor solenoid valve check performed 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 variation of pump motor switch voltage drop during or after the pump motor operation becomes larger than the specified value, the pump motor operation is stopped and this DTC is set.

PROBABLE CAUSES

Current trouble
^ Fusible link malfunction
^ Damaged wiring harness and connectors
^ Abnormality in battery or generator
^ ASC-ECU malfunction

Past trouble
^ Perform the diagnosis with a particular emphasis on the wiring harness and connector failures in the ASC-ECU motor power supply circuit (A-05 ASC-ECU connector terminal No. 1) and in the ground circuit (A-05 ASC-ECU connector terminal No. 16 and 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 A
^ MB991997: ASC check harness

STEP 1. Using scan tool MB991958, diagnose the CAN bus lines.
Using scan tool MB991958, diagnose the CAN bus lines.
Q: Is the check result normal?
YES: Go to Step 3.
NO: Repair the CAN bus lines (Refer to CAN Bus Diagnosis table Can Bus Diagnostics Table). On completion, go to Step 2.

STEP 2. DTC recheck after repairing the CAN bus line
Q: Is DTC C1073 set?
YES: Go to Step 3.
NO: The procedure is complete.

STEP 3. Battery check
Refer to Battery Test Battery Test.
Q: Is the battery in good condition?
YES: Go to Step 4.
NO: Replace the battery. Then go to Step 11.

STEP 4. Charging system check
Refer to Output Current Test Output Current Test.
Q: Is the charging system in good condition?
YES: Go to Step 5.
NO: Repair or replace the charging system component(s). Then go to Step 11.

STEP 5. Connector check: A-05 ASC-ECU connector
Q: Is the check result normal?
YES: Go to Step 6.
NO: Repair the defective connector. Then go to Step 11.

STEP 6. Fusible link check: Check the fusible link No. 26.
Visually check for open circuit in the fusible link No.26.
Q: Is the check result normal?
YES: Go to Step 8.
NO: Go to Step 7.

STEP 7. Resistance measurement at A-05 ASC-ECU connector

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

NOTE: Do not connect the special tool to ASC-ECU.

2) Measure the voltage between the terminal No. 1 and the body ground.
OK: Battery positive voltage
Q: Is the check result normal?
YES: Go to Step 9.
NO: The open circuit may be present in the power supply circuit. Repair the wiring harness between the A-05 ASC-ECU connector terminal No.1 and the fusible link No.26. Then go to Step 11.

STEP 9. Resistance measurement at A-05 ASC-ECU connector

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

NOTE: Do not connect the special tool to ASC-ECU.

2) Measure the resistance between the terminal No. 16 and the body ground as well as between the terminal No. 47 and the body ground.
OK: Continuity exists (2 ohms or less)
Q: Is the check result normal?
YES: Go to Step 10.
NO: An open circuit may be present in the ground circuit. Repair the wiring harness between the A-05 ASC-ECU connector terminal No.16 and the body ground, and between the A-05 ASC-ECU connector terminal No.47 and the body ground. Then go to Step 11.

STEP 10. Check whether the DTC is reset.
1) Erase the DTC.
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 hydraulic unit (incorporates in ASC-ECU). Then go to Step 11.
NO: Intermittent malfunction.

STEP 11. Check whether the DTC is reset.
1) Erase the DTC.
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: Return to Step 1.
NO: This diagnosis is complete.