Active Stability Control System (ASC)

DTC U0401 Engine signal malfunction detected

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 Line Diagnostics Flow.
- If DTC U0401 is set in ASC-ECU, always diagnose the CAN bus line. If there is any fault in the CAN bus lines, an incorrect DTC may be set. In this case, the set DTC is not highly reliable.
- Before replacing the ECU, ensure that the communication circuit is normal.

OPERATION

Engine-related signals are sent or received to and from between ASC-ECU and engine control module (ECM) via CAN bus lines.

DTC SET CONDITIONS

This DTC is set when the engine control module (ECM) malfunction has been detected.

PROBABLE CAUSES

- Malfunction of engine system
- Malfunction of engine control module (ECM)
- Malfunction of ASC-ECU
- External noise interference

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

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

Use scan tool to diagnose the CAN bus lines.

Q. Is the check result normal?

YES Go to Step 2.
NO Repair the CAN bus lines CAN Bus Diagnostics Chart).
On completion, go to Step 5.
STEP 2. Using scan tool MB991958, check the DTC

Use scan tool to check that any DTC other than the DTC U0401 is set in ASC-ECU.

Q. Is the DTC set?

YES Troubleshoot the relevant DTC, and then go to Step 5.
NO Go to Step 3.
STEP 3. Using scan tool MB991958, check the other system DTC

Use scan tool to check that the DTC is set by the engine control module (ECM).

Q. Is the DTC set?

YES Troubleshoot the relevant DTC, and then go to Step 5.
NO Go to Step 4.
STEP 4. Check whether the DTC is reset.

Erase the DTC.

Q. Is DTC U0401 set?

YES Replace the hydraulic unit (integrated with ASC-ECU) (Refer to Active Stability Control System (ASC)), and then go to Step 5.
NO Intermittent malfunction How to Cope With Intermittent Malfunctions).
STEP 5. Check whether the DTC is reset.

Erase the DTC.

Q. Is DTC U0401 set?

YES Return to Step 1.
NO The procedure is complete.