CODE No. U0121 ABS/ASC CAN timeout

caution

If diagnosis code No. U0121 is set in the BSW-ECU (master), always diagnose the CAN bus line.
Before replacing the ECU, ensure that the power supply circuit, the earth circuit and the communication circuit are normal.

OPERATION

The BSW-ECU (master) communicates with the ASC-ECU via the gateway-ECU and CAN bus lines.

CHECK CONDITION

Ignition switch is in the ON position.

DIAGNOSTIC FUNCTION AND JUDGEMENT CRITERIA

If the BSW-ECU (master) cannot receive any signal from the ASC-ECU for at least 2.5 seconds, the ECU sets diagnosis code No. U0121.

PROBABLE CAUSES

Power supply to the ASC-ECU fails
Malfunction of the ASC-ECU
Power supply to the gateway-ECU fails
Malfunction of the gateway-ECU
Malfunction of the BSW-ECU (master)
Malfunction of the CAN bus

DIAGNOSIS PROCEDURE

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

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

Q. Is the check result normal?

Go to Step 2.

Repair the CAN bus line (Refer to GROUP 54C - Troubleshooting

STEP 2. M.U.T.-III other system diagnosis code

Check that the other ECU performing CAN communication with ASC-ECU sets diagnosis code No. U0121 [Refer to GROUP 54C - CAN Communication-related Diagnosis Code (U-code) Table

Q. Is the diagnosis code set?

Go to Step 3.

Go to Step 4.

STEP 3. Check whether the diagnosis code is set again.

Check again if the diagnosis code is set in the BSW-ECU (master).

(1)Erase the diagnosis code.

(2)Turn the ignition switch from "LOCK" (OFF) position to "ON" position.

(3)Check if diagnosis code is set.

Q. Is the diagnosis code set?

Replace the ASC-ECU.

The trouble can be an intermittent malfunction such as a poor connection or open circuit in the CAN bus lines between the ASC-ECU and the BSW-ECU (master) (GROUP 00 - How to use Troubleshooting/inspection Service Points - How to Cope with Intermittent Malfunction).

STEP 4. M.U.T.-III other system diagnosis code

Check if diagnosis code No. U0146 is set in the ETACS-ECU.

Q. Is the diagnosis code set?

Troubleshoot the ETACS-ECU.

Go to Step 5.

STEP 5. M.U.T.-III other system diagnosis code

Check if diagnosis code No. U1073 is set in the gateway-ECU.

Q. Is the diagnosis code set?

Troubleshoot the gateway-ECU (Refer to 54C - Troubleshoot <GATEWAY> - Diagnosis Code Chart

Go to Step 6.

STEP 6. Check whether the diagnosis code is set again.

Check again if the diagnosis code is set in the BSW-ECU (master).

(1)Erase the diagnosis code.

(2)Turn the ignition switch from the LOCK (OFF) position to the ON position.

(3)Check if the diagnosis code is set.

Q. Is the diagnosis code set?

Replace the BSW-ECU (master).

Intermittent malfunction is suspected (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to cope with Intermittent Malfunction).