Electrical Power Steering System (EPS)

DTC U0001 Bus off

CAUTION:

- If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines Scan Tool Testing and Procedures ).
- Whenever ECU is replaced, ensure that the CAN bus lines are normal.

OPERATION

- Signals from the ECUs communicate with the electric power steering-ECU.

FUNCTION

- The signals from the ECUs communicate with the electric power steering-ECU for motor control.

TROUBLE JUDGMENT

Check Conditions

- IG1 voltage: 10 V or more

Judgment Criterion

- The signals from the ECUs cannot communicate (bus off), and the microcomputer determines that there is a problem in the system.

Fail Safe, Back Up Function

- The electric power steering-ECU illuminates the electric power steering warning display, and sets the DTC U0001 to limit assist operation.

PROBABLE CAUSES

- Malfunction of CAN bus line
- Malfunction of the electric power steering-ECU
- Malfunction of the engine control module (ECM)
- Malfunction of the ETACS-ECU
- Malfunction of the ABS-ECU [vehicles with ABS]
- Malfunction of the ASC-ECU [vehicles with ASC]

DIAGNOSIS

Required Special Tools:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)

STEP 1. M.U.T.-III CAN bus diagnostics

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

Q. Is the check result normal?

YES Go to Step 3.
NO Repair the CAN bus lines CAN Bus Diagnostics Chart). On completion, go to Step 2.
STEP 2. DTC recheck after resetting CAN bus lines

(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 U0001 set?

YES Go to Step 3.
NO This diagnosis is complete.
STEP 3. 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 U0001 set?

YES Replace the electric power steering-ECU (Refer to Service and Repair). Then go to Step 4.
NO Intermittent malfunction How to Cope With Intermittent Malfunctions).
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 U0001 set?

YES Return to Step 1.
NO This diagnosis is complete.