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Code No. C1276 Valve power supply circuit
Code No. C1278 Valve power circuit stuck off
Code No. C1279 Valve power circuit stuck on
 
 
caution
  • If there is any problem in the CAN bus lines, an incorrect diagnostic trouble code may be stored. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ).
  • Whenever ECU is replaced, ensure that the CAN bus lines are normal.
  • When the hydraulic unit (integrated with ASC-ECU) is replaced, always carry out the calibration of the steering wheel sensor and the G and yaw rate sensor (Refer to and ).
 
 
OPERATION
  • The ASC-ECU contains the power supply circuit (+BV terminal) for the solenoid valve. The solenoid valve is energized by the valve relay, which is incorporated in the ASC-ECU.
  • The valve relay, which is incorporated in the ASC-ECU, is always ON except for during the initial check at electric motor switch is turned ON as well as for during the system check that is periodically repeated. While the system is active, the power is supplied to the solenoid valve at all times.
 
 
DIAGNOSTIC TROUBLE CODE SET CONDITIONS
These diagnostic trouble codes will be stored under the cases below.
Code No. C1276 Valve power supply circuit
  • The ECU monitors the power supply voltage to the solenoid valve. If the voltage is lower than the predetermined value, the ECU stores this diagnostic trouble code as a failure in the valve power supply circuit.
Code No. C1278 Valve power circuit stuck off
  • When the solenoid valve is not energized even after the solenoid valve relay is turned ON, the ECU determines that the solenoid valve relay stuck OFF and stores this diagnostic trouble code.
Code No. C1279 Valve power circuit stuck on
  • When the solenoid valve is energized even after the solenoid valve relay is turned OFF, the ECU determines that the solenoid valve relay stuck ON and stores this diagnostic trouble code.
 
 
PROBABLE CAUSES
Current trouble
  • Battery failure
  • Damaged harness wires and connectors
  • Malfunction of ASC-ECU
Past trouble
  • Carry out diagnosis with particular emphasis on wiring harness and connector failures in the power supply circuit (+ BV terminal) to ASC-ECU solenoid valve or ground circuit (terminals GND1 and GND2). For diagnosis procedures, refer to How to treat past trouble (GROUP 00 - How to Use Troubleshooting/Inspection Service Points ).
 
 
DIAGNOSIS
STEP 1. Using scan tool MB991958, diagnose the CAN bus lines.
Use the scan tool MB991958 to diagnose the CAN bus lines.
Is the check result normal?
Go to Step 3.
Repair the CAN bus lines. (Refer to GROUP 54C - CAN Bus Line Trouble Symptom Chart .) On completion, go to Step 2.
 
STEP 2. Diagnostic trouble code recheck after resetting CAN bus lines
Is diagnostic trouble code No. C1276, C1278 or C1279 stored?
Go to Step 3.
This diagnosis is complete.
 
STEP 3. Check the battery.
Refer to GROUP 54A - Battery Test .
Is the auxiliary battery normal?
Go to Step 4.
Charge or replace the battery. Then go to Step 7.
 
STEP 4. Measure the resistance at the ASC-ECU connector.
(1) Connector check: ASC-ECU connector
(2) Disconnect the connector and measure at the wiring harness side.
(3) Measure the resistance between +BV terminal and body ground.
OK: No continuity
Is the check result normal?
Go to Step 5.
The power supply circuit may be short. Repair the wiring harness wires or connectors between the ACS-ECU connector +BV terminal and the fusible links, or replace the fusible links. Then go to Step 7.
 
STEP 5. Measure the voltage at the ASC-ECU connector.
(1) Disconnect the connector and measure at the wiring harness side.
(2) Measure the voltage between +BV terminal and body ground.
OK: Battery voltage
Is the check result normal?
Go to Step 6.
The power supply circuit may be open. Repair the wiring harness wires or connectors between the ACS-ECU connector +BV terminal and the fusible links. Then go to Step 7 .
 
STEP 6. Measure the resistance at the ASC-ECU connector.
(1) Disconnect the connector and measure at the wiring harness side.
(2) Measure the resistance between terminals GND1 or GND2 and body ground.
OK: Continuity exists (2 Ω or less).
Is the check result normal?
Go to Step 7.
An open circuit may be present in the ground circuit. Repair the wiring harness wires between ASC-ECU connector terminal GND1 or GND2 and body ground. Then go to Step 7.
 
STEP 7. Check whether the diagnostic trouble code is stored again.
Check again if the diagnostic trouble code is stored.
(1) Erase the diagnostic trouble code.
(2) Ignition switch: LOCK (OFF) position to ON
(3) Drive the vehicle until the vehicles speed reaches 20 km/h.
Is diagnostic trouble code No. C1276, C1278 or C1279 stored?
Replace the hydraulic unit (integrated with ASC-ECU). (Refer to .)
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).