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 diagnosis code may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C - Troubleshooting
).
- Whenever ECU is replaced, ensure that the CAN bus lines are normal.
- When the hydraulic unit assembly (integrated with ASTC-ECU) is replaced, always carry out the calibration of the steering wheel sensor and the G sensor (Refer to
).
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OPERATION
- The ASTC-ECU contains the power supply circuit (+BV terminal) for the solenoid valve. The solenoid valve is energised by the valve relay, which is incorporated in the ASTC-ECU.
- The valve relay, which is incorporated in the ASTC-ECU, is always ON except for during the initial check at ignition 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.
DIAGNOSIS CODE SET CONDITIONS
These diagnosis codes will be set 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 sets this diagnosis code as a failure in the valve power supply circuit.
Code No. C1278 Valve power circuit stuck off
- 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 Valve power circuit stuck on
- 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
- Battery failure
- Damaged harness wires and connectors
- Malfunction of the hydraulic unit assembly (integrated with ASTC-ECU)
Past trouble
- Carry out diagnosis with particular emphasis on wiring harness and connector failures in the power supply circuit (+ BV terminal) to ASTC-ECU solenoid valve or earth circuit (terminals GND1 and GND2). For diagnosis procedures, refer to How to treat past trouble (GROUP 00 - How to Use Troubleshooting/Inspection Service Points
).
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STEP 1. M.U.T.-III CAN bus diagnosis
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Use the M.U.T.-III to diagnose the CAN bus lines.
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Q.
Is the check result normal?
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Go to Step 3.
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Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Line Trouble Symptom Chart ). On completion, go to Step 2.
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STEP 2. Diagnosis code recheck after resetting CAN bus lines
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Q.
Is diagnosis code No. C1276, C1278 or C1279 set?
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Go to Step 3.
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This diagnosis is complete.
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STEP 3. Check the battery.
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Refer to GROUP 54A - Battery Test .
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Q.
Is the auxiliary battery normal?
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Go to Step 4.
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Charge or replace the battery. Then go to Step 7.
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STEP 4. Measure the resistance at the ASTC-ECU connector.
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(1)Connector check: ASTC-ECU connector
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(2)Disconnect the connector and measure at the wiring harness side.
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(3)Measure the resistance between +BV terminal and body earth. OK: No continuity
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Q.
Is the check result normal?
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Go to Step 5.
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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.
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STEP 5. Measure the voltage at the ASTC-ECU connector.
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(1)Disconnect the connector and measure at the wiring harness side.
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(2)Measure the voltage between +BV terminal and body earth. OK: Battery voltage
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Q.
Is the check result normal?
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Go to Step 6.
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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
.
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STEP 6. Measure the resistance at the ASTC-ECU connector.
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(1)Disconnect the connector and measure at the wiring harness side.
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(2)Measure the resistance between terminals GND1 or GND2 and body earth. OK: Continuity exists (2 Ω or less).
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Q.
Is the check result normal?
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Go to Step 7.
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An open circuit may be present in the earth circuit. Repair the wiring harness wires between ASTC-ECU connector terminal GND1 or GND2 and body earth. Then go to Step 7.
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STEP 7. Check whether the diagnosis code is set again.
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Check again if the diagnosis code is set.
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(1)Erase the diagnosis code.
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(2)Ignition switch: "LOCK" (OFF) position to "ON"
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(3)Drive the vehicle until the vehicles speed reaches 20 km/h.
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Q.
Is diagnosis code No. C1276, C1278 or C1279 set?
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Replace the hydraulic unit assembly (integrated with ASTC-ECU) (Refer to ).
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The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).
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