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 - CAN Bus Diagnostics Table ).
Before replacing the ECU, ensure that the communication circuit is normal.
OPERATION
The ASC-ECU contains the power supply circuit (terminal No.25) for the solenoid
valve. The solenoid valve is energised by the solenoid valve relay, which is incorporated in
the ASC-ECU.
The valve relay, which is incorporated in the ASC-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 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
ASC-ECU malfunction
Past trouble
Carry out diagnosis with particular emphasis on connector(s) or
wiring harness in the power supply circuit (terminal No.25) to the ASC-ECU solenoid valve and
earth circuit (terminal No.13 and No.38). For diagnosis procedures, refer to How to treat past
trouble (GROUP 00 - How to Use Troubleshooting/How to Cope with Intermittent
Malfunctions ).
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 Diagnostics 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. Auxiliary battery check
Refer to GROUP 54A - Battery Test .
Q.
Is the battery in good condition?
Go to Step 4.
Charge or replace the auxiliary battery. Then go to Step 10.
STEP 4. Connector check: A-14 ASC-ECU connector
Q.
Is the check result normal?
Go to Step 5.
NO : Repair the defective connector. Then go to Step 10.
STEP 5. Fusible link check: Check the fusible link No.24.
Visually check for open circuit in the fusible link No.24.
Q.
Is the check result normal?
Go to Step 7.
Go to Step 6.
STEP 6. Resistance measurement at A-14 ASC-ECU connector
(1)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335)
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 (MB992335) to ASC-ECU.
(2)Measure the resistance between the terminal No.25 and the body earth. OK: No continuity
Q.
Is the check result normal?
Replace the fusible link No.24. Then go to Step 10.
The short circuit may be present in the power supply circuit. Repair the wiring
harness between the A-14 ASC-ECU connector terminal No.25 and the fusible link No.24, and then
replace the fusible link No.24. Then go to Step 10.
STEP 7. Voltage measurement at the A-14 ASC-ECU connector
(1)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335)
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 (MB992335) to ASC-ECU.
(2)Measure the voltage between the terminal No.25 and the body earth. OK: Approximately system voltage
Q.
Is the check result normal?
Go to Step 8.
The open circuit may be present in the power supply circuit. Repair the wiring
harness between the A-14 ASC-ECU connector terminal No.25 and the fusible link No.24. Then go
to Step 10.
STEP 8. Resistance measurement at A-14 ASC-ECU connector
(1)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335)
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 (MB992335) to ASC-ECU.
(2)Measure the resistance between the terminal No.13 and the body earth, and between the
terminal No.38 and the body earth OK: Continuity exists (2 Ω or less)
Q.
Is the check result normal?
Go to Step 9.
An open circuit may be present in the earth circuit. Repair the wiring harness
between the A-14 ASC-ECU connector terminal No.13 and the body earth, and between the A-14 ASC-ECU
connector terminal No.38 and the body earth. Then go to Step 10.
STEP 9. Check whether the diagnosis code is reset.
Erase the diagnosis code.
Q.
Is the diagnosis code No.C1276, C1278 or C1279 set?
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ).
Then go to Step 10.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/How
to Cope with Intermittent Malfunctions ).
STEP 10. Check whether the diagnosis code is reset.
Erase the diagnosis code.
Q.
Is the diagnosis code No.C1276, C1278 or C1279 set?
)
)
)
Go to Step 3.
Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table 
).
On completion, go to Step 2.
: Repair the defective connector. Then go to Step 10.)
)
)
