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 (Refer to GROUP 54C, Trouble code diagnosis ).
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 energised 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 (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

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. M.U.T.-III CAN bus diagnostics

Use scan tool to diagnose the CAN bus lines.

Q. Is the check result normal?

	Go to Step 3.

	Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics table ). On completion, go to Step 2.

STEP 2. Check whether the DTC is reset.

Q. Is DTC C1073 set?

	Go to Step 3.

	The procedure is complete.

STEP 3. Battery check

Refer to GROUP 54A - Battery Test

Q. Is the battery in good condition?

	Go to Step 4.

	Charge or replace the battery.

STEP 4. Charging system check

Refer to GROUP 16 - Output Current Test

Q. Is the charging system in good condition?

	Go to Step 5.

	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?

	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?

	Go to Step 8.

	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 then measure the resistance at the special tool connector side.

note

Do not connect the special tool to ABS-ECU.

(2)Disconnect the fusible link No.26.
(3)Resistance between the terminal No.13 and the body earth.
OK: No continuity

Q. Is the check result normal?

Replace the fusible link No.26. Then go to Step 11.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-03 ABS-ECU connector terminal No.13 and the fusible link No.26, and then replace the fusible link No.26. Then go to Step 11.

STEP 8. Voltage measurement at the 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: Approximately battery voltage

Q. Is the check result normal?

Go to Step 9.

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 Ω or less)

Q. Is the check result normal?

Go to Step 10.

An open circuit may be present in the earth 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 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?

	Replace the hydraulic unit (ABS-ECU) (Refer to ). Then go to Step 11.

	Intermittent malfunction (Refer to GROUP 00 - How to Cope with 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?

	Return to Step 1.

	The procedure is complete.