Code No. U0168: WCM CAN time-out


caution If diagnosis code No.U1109 is set in the A/C-ECU, diagnose the CAN main bus line.
caution Whenever the ECU is replaced, ensure that the communication circuit is normal.

TROUBLE JUDGMENT
The A/C-ECU receives air conditioner control-related signals from the WCM via the CAN bus lines. If the ECU cannot receive any of the air conditioner control-related signals from the WCM, diagnosis code U0168 will be stored.

COMMENTS ON TROUBLE SYMPTOM
Current trouble
  • Connector(s) or wiring harness in the CAN bus lines between the WCM and the A/C-ECU, the power supply system to the WCM, the WCM itself, or the A/C-ECU may be faulty.
Past trouble
  • Carry out diagnosis with particular emphasis on connector(s) or wiring harness in the CAN bus lines between the A/C-ECU and the WCM, and the power supply system to the WCM. For diagnosis procedures, refer to "How to treat past trouble" (Refer to GROUP 00 - How to Treat Past Trouble ).?
    note For a past trouble, you can not find it by the M.U.T.-III CAN bus diagnostics even if there is any failure in CAN bus lines. In this case, refer to GROUP 00, How to Cope with Intermittent Malfunction and check the CAN bus lines. You can narrow down the possible cause of the trouble by referring to the diagnosis code, which is set regarding the CAN communication-linked ECUs (Refer to GROUP 54C - CAN Bus Line Diagnostic Flow ).
    caution If the ignition switch is turned to the ON position without starting the engine, the diagnosis code U0168 (past trouble) may be set to the A/C-ECU after three minutes.

PROBABLE CAUSES

  • Damaged harness wires and connectors
  • Malfunction of WCM
  • Malfunction of the A/C-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostics
Use the M.U.T.-III to diagnose the CAN bus lines.

Q. Is the check result normal?
Go to Step 2.
Repair the CAN bus lines (Refer to GROUP 54C Troubleshooting ). On completion, go to Step 6.

STEP 2. M.U.T.-III other system diagnosis code
Check whether the WCM-related diagnosis code is set.

Q. Is the diagnosis code set?
Diagnose the WCM. Refer to .
Go to Step 3.

STEP 3. M.U.T.-III other system diagnosis code
Check if a diagnosis code, which relates to CAN communication-linked systems below, is set.

  • combination meter
    U0168: WCM-related time-out diagnosis code

Q. Is the diagnosis code set?
Go to Step 4.
Go to Step 5.

STEP 4. Check whether the diagnosis code is reset.
Recheck if the diagnosis code is set.
(1)Erase the diagnosis code.
(2)Ignition switch: LOCK (OFF) to ON
(3)Check if the diagnosis code is set.

Q. Is the diagnosis code set?
Replace the WCM, and then go to Step 6.
A poor connection, open circuit or other intermittent malfunction in the CAN bus line between the WCM and the A/C-ECU (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

STEP 5. Check whether the diagnosis code is reset.
Recheck if the diagnosis code is set.
(1)Erase the diagnosis code.
(2)Ignition switch: LOCK (OFF) to ON
(3)Check if the diagnosis code is set.

Q. Is the diagnosis code set?
Replace the A/C-ECU, and then go to Step 6.
A poor connection, open circuit or other intermittent malfunction in the CAN bus line between the WCM and the A/C-ECU (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

STEP 6. Check whether the diagnosis code is reset.
Recheck if the diagnosis code is set.
(1)Erase the diagnosis code.
(2)Ignition switch: LOCK (OFF) to ON
(3)Check if the diagnosis code is set.

Q. Is the diagnosis code set?
Return to Step 1.
The procedure is complete.