Electronic Control AWD

DTC U0121: ABS CAN timeout

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 receives the data (such as ABS sensor signal, ABS operation signal) via the CAN bus lines. If it cannot receive such data, it interrupts the system.

DTC SET CONDITIONS

If the following conditions are met when the system is activated, AWD-ECU gradually switches the control from AWD to FWD, flashes the AWD/LOCK indicators alternately, and sets the DTC U0121.

- IG1 voltage: 10 V or more

- ABS signal (such as wheel speed signal) cannot be received.

TROUBLESHOOTING HINTS

Current trouble

- Wiring harness or connector failure between ABS/ASC-ECU and the stoplight switch

- Malfunction of the ABS sensor

- Malfunction of the stoplight switch

- ABS/ASC-ECU malfunction

- AWD-ECU malfunction
Past trouble

- Refer to How to Use Troubleshooting - How to Treat Past Trouble How to Treat Past Trouble for proceeding the diagnostics.

DIAGNOSIS

Required Special Tools:

- 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 CAN Bus Diagnostics Chart). Then go to Step 2.
STEP 2. Scan tool MB991958 data list

Check the following data list (Refer to Data List Reference Table).

- Item 07: CAN system (ABS/ASC)

Q. Is the check result normal?

YES Go to Step 6.
NO Go to Step 3.
STEP 3. Scan tool MB991958 DTC of other systems

Check if a DTC, which relates to the CAN communication-linked systems below, is set.

- Engine
U0121: ABS/ASC timeout DTC

Q. Is the DTC set?

YES Go to Step 4.
NO Go to Step 5.
STEP 4. 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 U0121 set?

YES Troubleshoot the ABS system Anti-Lock Braking System (ABS) [Vehicles with ABS]), the ASC system
Reading and Clearing Diagnostic Trouble Codes [Vehicles with ASC]). Then go to Step 5.
NO Go to Step 6.
STEP 5. 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 U0121 set?

YES Replace AWD-ECU (Refer to Electronic Control AWD). Then go to Step 6.
NO The procedure is complete.
STEP 6. Check whether the DTC is reset.

Q. Is the DTC U0121 set?

YES Diagnose again from Step 1.
NO The procedure is complete.