DTC U0168: WCM Time-out

caution

If DTC U0168 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 the air conditioning control-related signals from the WCM-ECU via the CAN bus lines. If any of the air conditioning control-related signals from the WCM-ECU cannot be received, diagnostic trouble code U0168 is stored.

TECHNICAL DESCRIPTION (COMMENT)

Current trouble

Connector(s) or wiring harness in the CAN bus lines between the WCM-ECU and the A/C-ECU, the power supply system to the WCM-ECU, the WCM-ECU itself, or the A/C-ECU 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-ECU and the WCM-ECU, and the power supply system to the WCM-ECU. 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.

note

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

DIAGNOSIS

Required Special Tools:

MB991223: Harness Set
MB992006: Extra Fine Probe
MB991958: Scan Tool (M.U.T.-III Sub Assembly)

MB991824: V.C.I.
MB991827: M.U.T.-III USB Cable
MB991910: M.U.T.-III Main Harness A

STEP 1. Using scan tool MB991958, diagnose the CAN bus line

(1)

caution

To 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.

Q. 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-ECU diagnostic trouble code.

Check whether an WCM-ECU DTCs are set or not.

(1)Turn the ignition switch to the "ON" position.

(2)Check for WCM-ECU DTCs.

(3)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the DTC set?

	Go to Step 3.

	Diagnose the WCM-ECU (Refer to GROUP 42C, 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-ECU 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.

Q. 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.

Q. Is the DTC set?

	Replace the WCM-ECU. On completion, check that the DTC is not reset.

	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.

Q. Is the DTC set?

	Replace the A/C-ECU. On completion, check that the DTC is not reset.

	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 .)