Code No.C1276: Abnormality In Valve Relay System
Code No.C1278: Abnormality In Valve Relay System (Stuck Off)
Code No.C1279: Abnormality In Valve Relay System (Stuck ON)




caution
  • If there is any problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C, Trouble code diagnosis ).
  • Before replacing the ECU, ensure that the communication circuit is normal.

OPERATION

  • The ABS-ECU contains the power supply circuit (terminal No.24) for the solenoid valve. The solenoid valve is energised by the solenoid valve relay, which is incorporated in the ABS-ECU.
  • The valve relay, which is incorporated in the ABS-ECU, is always energising the solenoid valve unless the initial check is in progress when the ignition switch is turned on, or the recurrent system check is in progress.

DIAGNOSIS CODE SET CONDITIONS
These diagnosis codes will be set under the cases below:
Code No.C1276
  • The ABS-ECU monitors the power supply voltage to the solenoid valve. If the voltage, compared to the power supply voltage to the ECU, is lower than the predetermined value, the ECU sets this diagnosis code as a failure in the valve relay circuit.
Code No.C1278
  • When the solenoid valve is not energised even after the solenoid valve relay is turned ON, the ECU determines that the solenoid valve relay stuck OFF and sets this diagnosis code.
Code No.C1279
  • When the solenoid valve is energised even after the solenoid valve relay is turned OFF, the ECU determines that the solenoid valve relay stuck ON and sets this diagnosis code.

PROBABLE CAUSES
Current trouble
  • Damaged wiring harness and connectors
  • ABS-ECU malfunction
Past trouble
  • Carry out diagnosis with particular emphasis on connector(s) or wiring harness in the power supply circuit (terminal No.24) to the ABS-ECU solenoid valve and earth circuit (terminal No.23 and No.26). For diagnosis procedures, refer to How to treat past trouble (GROUP 00 - How to Cope with Intermittent Malfunction ).

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostics
Use M.U.T.-III 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 Diagnosis table ). On completion, go to Step 2.

STEP 2. Check whether the diagnosis code is reset.

Q. Is the diagnosis code No.C1276, C1278 or C1279 set?
Go to Step 3.
This diagnosis is complete.

STEP 3. Battery check
Refer to GROUP 54A - Battery Test .

Q. Is the battery in good condition?
Go to Step 4.
Replace the battery. Then go to Step 11.

STEP 4. Charging system check
Refer to GROUP 16 - Charging System .

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-05 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 the fusible link No.5.
Visually check for open circuit in the fusible link No.5.

Q. Is the check result normal?
Go to Step 8.
Go to Step 7.

STEP 7. Resistance measurement at A-05 ABS-ECU connector
(1)Remove the fusible link No.5.

(2)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991951) to the harness-side connector, and then measure the resistance at the special tool connector side.
note Do not connect the special tool ABS check harness (MB991951) to ABS-ECU.

(3)Measure the resistance between the terminal No.24 and the body earth.
OK: No continuity

Q. Is the check result normal?

Replace the fusible link No.5. Then go to Step 11.

The short circuit may be present in the power supply circuit. Repair the wiring harness between the A-05 ABS-ECU connector terminal No.24 and the fusible link No.5, and then replace the fusible link No.5. Then go to Step 11.

STEP 8. Voltage measurement at the A-05 ABS-ECU connector

(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991951) to the harness-side connector, and then measure the voltage at the special tool connector side.
note Do not connect the special tool ABS check harness (MB991951) to ABS-ECU.

(2)Measure the voltage between the terminal No.24 and the body earth.
OK: System 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-05 ABS-ECU connector terminal No.24 and the fusible link No.5. Then go to Step 11.

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

(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991951) to the harness-side connector, and then measure the resistance at the special tool connector side.
note Do not connect the special tool ABS check harness (MB991951) to ABS-ECU.

(2)Measure the resistance between the terminal No.23 and the body earth, and between the terminal No.26 and the body earth
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-05 ABS-ECU connector terminal No.23 and the body earth, and between the A-05 ABS-ECU connector terminal No.26 and the body earth. Then go to Step 11.

STEP 10. Check whether the diagnosis code is reset.

Q. Is the diagnosis code No.C1276, C1278 or C1279 set?
Replace the hydraulic unit (integrated with 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 diagnosis code is reset.

Q. Is the diagnosis code No.C1276, C1278 or C1279 set?
Return to Step 1.
This diagnosis is complete.