Anti-Lock Braking System (ABS)

DTC C1073: Malfunction of motor drive circuit

CAUTION:

- If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines CAN Bus Diagnostics Chart).

- Whenever ECU is replaced, ensure that the CAN bus lines are normal.

CIRCUIT OPERATION

- ABS-ECU contains the power supply circuit (terminal No.13) for the pump motor.
The pump motor is energized by the motor switch, which is incorporated in ABS-ECU.

- The pump motor switch, which is incorporated in ABS-ECU, is always off unless the ABS operating or the motor solenoid valve check is activated when the vehicle is started.

- ABS-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 DTC is set.

PROBABLE CAUSES

Current trouble

- Fusible link malfunction

- Damaged wiring harness and connectors

- Abnormality in battery or generator

- ABS-ECU malfunction

Past trouble

- Carry out diagnosis with particular emphasis on wiring harness and connector failures between the power supply circuit (A-03 ABS-ECU connector terminal No.13) to the ABS-ECU motor and the ground circuit (A-03 ABS-ECU connector terminal No.1). For diagnosis procedures, refer to How to treat past trouble 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

- MB991974: ABS check harness

STEP 1. Using scan tool MB991958, diagnose the CAN bus lines.

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 CAN Bus Diagnostics Chart).
On completion, go to Step 2.
STEP 2. Check whether the DTC is reset.

Q. Is DTC C1073 set?

YES Go to Step 3.
NO The procedure is complete.
STEP 3. Battery check

Battery Test.

Q. Is the battery in good condition?

YES Go to Step 4.
NO Charge or replace the battery.
STEP 4. Charging system check

Generator Output Line Voltage Drop 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-03 ABS-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 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-03 ABS-ECU connector

(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and measure the voltage at the special tool connector side.
NOTE:
Do not connect the special tool to ABS-ECU.

(2)Measure the voltage between terminal No.13 and body ground.
OK: Battery 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-03 ABS-ECU connector terminal No.1 and the fusible link No.26. Then go to Step 11.

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

(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the resistance at the special tool connector side.
NOTE:
Do not connect the special tool to ABS-ECU.

(2)Measure the resistance between terminal No.1 and body ground, and between terminal No.14 and 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-03 ABS-ECU connector terminal No.1 and the body ground, and between the A-03 ABS-ECU connector terminal No.14 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 higher.
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 (integrated with ABS-ECU) (Refer to Anti-Lock Braking System (ABS)). Then go to Step 11.
NO Intermittent malfunction How to Cope With Intermittent Malfunctions).
STEP 11. Check whether the DTC is reset.

(1)Erase the DTC.

(2)Drive the vehicle at 12 mph (20 km/h) or higher.
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 The procedure is complete.