ABS

DTC C1271: Motor Circuit Failure

Solenoid Valve And Motor Power Supply Circuit Connector: A-02:

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.

CIRCUIT OPERATION
^ The ABS-ECU contains the power supply circuit (terminal 13) for the pump motor. The pump motor is energized by the motor relay, which is integrated in the ABS-ECU.
^ The motor relay, which is integrated in the ABS-ECU, is always off unless the motor solenoid valve check is activated when the vehicle is started.
^ The ABS-ECU activates the pump motor by turning on the ECU built-in motor relay when the ABS is working.

ABS DTC SET CONDITIONS
This diagnostic trouble code will be set under the cases below.
^ When the voltage supplied to the pump motor is too low.
^ When the voltage supplied to the pump motor is too high.
^ When the ABS-ECU judges that the voltage is supplied to the pump motor while the pump motor is stopped.

TROUBLESHOOTING HINTS (The most likely causes for these DTCs are to set are:)

Current trouble
^ Damaged wiring harness or connector
^ Malfunction of the hydraulic unit (integrated with ABS-ECU)

Past trouble
^ Carry out diagnosis with particular emphasis on connector(s) or wiring harness between the power supply circuit (terminal 13) to the ABS-ECU motor or ground circuit (terminal 1). For diagnosis procedures, refer to "How to treat past trouble".

DIAGNOSIS

Required Special Tools:
^ MB991958: Scan Tool (M.U.T.-III Sub Assembly)
^ MB991824: 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 line.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

(1) Connect scan tool MB991958 to the data link connector.
(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the CAN bus line found to be normal?
YES: Go to Step 3.
NO: Repair the CAN bus line, refer to Diagnosis. Then go to Step 2.

STEP 2. Recheck for diagnostic trouble code.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

(1) Turn the ignition switch to the "ON" position.
(2) Erase the DTC.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
(4) Turn the ignition switch to the "ON" position.
(5) Check if the DTC is set.
(6) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is DTC C1271 set?
YES: Go to Step 3.
NO: The procedure is complete.

STEP 3. Measure the voltage at ABS-ECU connector A-02.

(1) Disconnect the connector A-02, and connect special tool MB991974 to the wiring harness-side connector.

NOTE: Do not connect special tool MB991974 to the ABS-ECU.

(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal 13 and ground. It should be approximately 12 volts (battery positive voltage).
Q: Is the voltage approximately 12 volts (battery positive voltage)?
YES: Go to Step 5.
NO: Go to Step 4.

STEP 4. Check ABS-ECU connector A-02 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is ABS-ECU connector A-02 damaged?
YES: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. Then go to Step 8.
NO: An open or short circuit may be present in the solenoid valve power supply circuit. Repair the wiring harness between ABS-ECU connector A-02 terminal 13 and fusible link No.3.Then go to Step 8.

STEP 5. Measure the resistance at ABS-ECU connector A-02.

(1) Disconnect the connector A-02, and connect special tool MB991974 to the wiring harness-side connector.

NOTE: Do not connect special tool MB991974 to the ABS-ECU.

(2) Measure the resistance between terminal 1 and ground. It should be 2 ohms or less.
Q: Is the measured resistance 2 ohms or less?
YES: Go to Step 7.
NO: Go to Step 6.

STEP 6. Check ABS-ECU connector A-02 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is ABS-ECU connector A-02 damaged?
YES: Repair or replace the damaged component(s). Refer to Harness Connector Inspection.
Then go to Step 8.
NO: An open circuit may be present in the ground circuit. Repair the wiring harness between ABS-ECU connector A-02 terminal 13 and the body ground. Then go to Step 8.

STEP 7. Recheck for diagnostic trouble code.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958. Check again if the DTC is set.

(1) Turn the ignition switch to the "ON" position.
(2) Erase the DTC.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
(4) Turn the ignition switch to the "ON" position.
(5) Check if the DTC is set.
(6) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is DTC C1271 set?
YES: Replace the hydraulic unit (integrated with ABS-ECU). Then go to Step 8.
NO: It can be assumed that this malfunction is intermittent.
Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction.

STEP 8. Recheck for diagnostic trouble code.