Electronic Control

DTC U0001: Malfunction of bus-off

CAUTION:
^ If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, always diagnose the CAN bus lines.
^ Before replacing the ECU, ensure that the communication circuit is normal.

OPERATION
AWD-ECU monitors the CAN C-bus off interruption, and if any abnormality occurs, it interrupts the system.

DTC SET CONDITIONS
If the following conditions are met when the system is in operation (always), AWD-ECU gradually switches the control from AWD to FWD, flashes the AWD/LOCK indicators alternately, and sets the DTC No. U0001.

^ IG1 voltage: 10 V or more
^ When CAN C-bus off interruption is detected

TROUBLESHOOTING HINTS

Current trouble
^ Wiring harness or connector failure of CAN bus line
^ AWD-ECU malfunction

Past trouble
^ Intermittent wiring harness or connector failure

NOTE: For diagnosis procedures, refer to "How to treat past trouble".

DIAGNOSIS
^ MB991958: Scan Tool (M.U.T.-III Sub Assembly)
^ MB991824: Vehicle Communication Interface
^ MB991827: M.U.T.-III USB Cable
^ MB991910: M.U.T.-III Main Harness A

STEP 1. Scan tool MB991958 CAN bus diagnostics
Use scan tool MB991958 to diagnose the CAN bus lines.

Q:Is the check result normal?
YES: Go to Step 2.
NO: Repair the CAN bus line. Then go to Step 3.

STEP 2. Check whether the DTC is reset.
(1) Erase the DTC.
(2) Turn the ignition switch from the LOCK (OFF) position to the ON position.
(3) Check if the DTC is set.

Q:Is the DTC No. U0001 set?
YES: Replace AWD-ECU. Then go to Step 3.
NO: The trouble can be an intermittent malfunction such as loose connector fit, wiring harness open circuit.

STEP 3. Check whether the DTC is reset.

Q:Is the DTC No. U0001 set?
YES: Diagnose again from Step 1.
NO: This diagnosis is complete.