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 CAN Bus Diagnostics Chart ).
- Whenever ECU is replaced, ensure that the CAN bus lines are normal.

OPERATION

Signals from the ECUs communicate with the EPS-ECU.

FUNCTION

The signals from the ECUs communicate with the EPS-ECU for motor control.

TROUBLE JUDGEMENT

Check Conditions

IG1 voltage: 10 V or more

Judgement 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 EPS-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 EPS-ECU
- Malfunction of the engine control module (ECM)
- Malfunction of the ETACS-ECU
- Malfunction of the ASC-ECU

DIAGNOSIS

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

Use scan tool 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 EPS-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.