C1278

DTC C1278/C1279 Valve Relay System

Solenoid Valve and Motor Power Supply 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.

CIRCUIT OPERATION
^ The ABS-ECU contains the power supply circuit (terminal 1) for the solenoid valve. The solenoid valve is energized by the valve relay, which is integrated in the ABS-ECU.
^ The valve relay, which is integrated in the ABS-ECU, is always energizing the solenoid valve unless the initial check is in progress when the ignition switch is turned on.

ABS DTC SET CONDITIONS
These diagnostic trouble codes will be set under the cases below.

DTC C1278 (Valve relay OFF failure)
^ After the ABS-ECU turned on the valve relay, the solenoid valve is not energized (valve relay OFF failure).

DTC C1278 (Valve relay ON failure)
^ After the ABS-ECU turned off the valve relay, the solenoid valve still remains energized (valve relay ON failure).

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

Correct 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 1) to the ABS-ECU solenoid valve or ground circuit (terminal 2). For diagnosis procedures, refer to "How to cope with past trouble". Initial Inspection and Diagnostic Overview

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
^ MB991970: 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. 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 C1278 or C1279 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 ABS Check Harness (MB991970) to the wiring harness-side connector.

NOTE: Do not connect special tool ABS Check Harness (MB991970) to the ABS-ECU.

(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal 1 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). 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 1 and fusible link No. 3. Then go to Step 8.

STEP 5. Measure the resistance at ABS-ECU connector A02.

(1) Disconnect the connector A-02, and connect special tool ABS Check Harness (MB991970) to the wiring harness-side connector.

NOTE: Do not connect special tool ABS Check Harness (MB991970) to the ABS-ECU.

(2) Measure the resistance between terminal 2 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). 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 2 and the body ground. Then go to Step 8.

STEP 7. Recheck for diagnostic trouble code.

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 C1278 or C1279 set?
YES: Go to Step 1.
NO: The procedure is complete.

DTC C1607: Trouble in ABS-ECU

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.

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

ABS DTC SET CONDITIONS
The ABS-ECU always monitors itself while the system is working. If the ECU detects any faults, it will set this DTC.

TROUBLESHOOTING HINTS (The most likely causes for these DTCs are to set are:)
^ Malfunction of the hydraulic unit (integrated with ABS-ECU)

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

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 2.
NO: Repair the CAN bus line. 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 C1607 set?
YES : Replace the hydraulic unit (integrated with ABS-ECU).
NO: The procedure is complete.