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DTC U0168: WCM/F.A.S.T. CAN timeout
 
 
cautionIf DTC U0168 is set in the A/C control panel, diagnose the CAN main bus line.
cautionWhenever the ECU is replaced, ensure that the communication circuit is normal.
 
 
 
 
TROUBLE JUDGMENT
The A/C control panel receives the air conditioning control-related signals from the WCM <Vehicles without KOS> or KOS-ECU<Vehicles with KOS> via the CAN bus lines. If any of the air conditioning control-related signals from the WCM <Vehicles without KOS> or KOS-ECU <Vehicles with KOS> cannot be received, diagnostic trouble code U0168 is set.
 
 
TECHNICAL DESCRIPTION (COMMENT)
Current trouble
  • Connector(s) or wiring harness in the CAN bus lines between the WCM <Vehicles without KOS> or KOS-ECU <Vehicles with KOS> and the A/C control panel, the power supply system to the WCM <Vehicles without KOS> or KOS-ECU <Vehicles with KOS>, the WCM <Vehicles without KOS> or KOS-ECU<Vehicles with KOS> itself, the A/C control panel may be defective.
Past trouble
  • If DTC U0168 is stored as a past trouble, carry out diagnosis with particular emphasis on wiring and connector(s) in the CAN bus line between the A/C control panel and the WCM <Vehicles without KOS> or KOS-ECU <Vehicles with KOS>, and the power supply system to the WCM <Vehicles without KOS> or KOS-ECU <Vehicles with KOS>. If the connectors and wiring are normal, and obviously the ECU is the cause of the trouble, replace the ECU. If in doubt, do not replace the ECU.
    noteFor a past trouble, you cannot find it by the scan tool CAN bus diagnostics even if there is a failure in CAN bus lines. In this case, refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ) and check the CAN bus lines. You can narrow down the possible cause of the trouble by referring to the DTC, which is set regarding the CAN communication-linked ECUs (Refer to GROUP 54C, Explanation about the scan too CAN bus diagnostics ).
 
 
TROUBLESHOOTING HINTS
  • Malfunction of the WCM <Vehicles without KOS>
  • Malfunction of the KOS-ECU <Vehicles with KOS>
  • Malfunction of the A/C control panel
  • Damaged wiring harness or connectors
 
 
DIAGNOSIS
STEP 1. Using scan tool MB991958, diagnose the CAN bus line
(1)
cautionTo prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
Connect scan tool MB991958. Refer to "How to connect the Scan Tool (M.U.T.-III) ."
(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the CAN bus line found to be normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C, Diagnosis ).
 
STEP 2. Using scan tool MB991958 read the WCM <Vehicles without KOS> or KOS-ECU <Vehicles with KOS> diagnostic trouble code.
Check whether an WCM <Vehicles without KOS> or KOS-ECU <Vehicles with KOS> DTCs are set or not.
(1) Turn the ignition switch to the "ON" position.
(2) Check for WCM <Vehicles without KOS> or KOS-ECU <Vehicles with KOS> DTCs.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC set?
Go to Step 3.
Diagnose the WCM <Vehicles without KOS> (Refer to GROUP 42C, Diagnostic Trouble Code ) or KOS-ECU <Vehicles with KOS> (Refer to GROUP 42B , Diagnostic Trouble Code ).
 
STEP 3. Using scan tool MB991958, check for any diagnostic trouble code.
Check if a DTC, which relates to CAN communication-linked systems below, is set.
  • ETACS-ECU
    DTC indicating a time-out error related to the WCM <Vehicles without KOS> or KOS-ECU <Vehicles with KOS> system
(1) Turn the ignition switch to the "ON" position.
(2) Check for a DTC related to the relevant system.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC set?
Go to Step 4.
Go to Step 5.
 
STEP 4. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Turn the ignition switch to the "ON" position.
(2) Check if the DTC is set.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC set?
Replace the WCM <Vehicles without KOS> or KOS-ECU <Vehicles with KOS>. On completion, check that the DTC is not set again.
There is an intermittent malfunction such as poor engaged connector(s) or open circuit (Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .)
 
STEP 5. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Turn the ignition switch to the "ON" position.
(2) Check if the DTC is set.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC set?
Replace the A/C control panel. On completion, check that the DTC is not set again.
There is an intermittent malfunction such as poor engaged connector(s) or open circuit (Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .)