Code No.U0121 ABS/ASC CAN timeout


caution
  • If the diagnosis code No. U0121 is set, be sure to diagnose the CAN bus line.
  • Before replacing the ECU, ensure that the power supply circuit, the earth circuit and the communication circuit are normal.

DIAGNOSTIC FUNCTION


When the LDW-ECU receives no signal from the ASC-ECU for 2.5 seconds or more, it will store diagnosis code No. U0121.

JUDGEMENT CRITERIA


When the LDW-ECU receives no signal from the ASC-ECU for 2.5 seconds or more, it will determine that the system is defective.

PROBABLE CAUSES



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 ). On completion, go to Step 2.

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


Check if diagnosis code is set to the ASC-ECU.

Q. Is the diagnosis code set?

Troubleshoot the ASC. Refer to GROUP 35C - Troubleshooting .

Go to Step 3

STEP 3. Check the M.U.T.-III Diagnosis code for other systems


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

Q. Is the diagnosis code set?

Go to Step 4

Go to Step 5

STEP 4. Check whether the diagnosis code is reset.


Check again if the diagnosis code is set to the LDW-ECU.
(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 LDW-ECU (GROUP 00 - How to use Troubleshooting/inspection Service Points - How to Cope with Intermittent Malfunction ).

STEP 5. Check whether the diagnosis code is reset.


Check again if the diagnosis code is set to the LDW-ECU.
(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 LDW-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 LDW-ECU (GROUP 00 - How to use Troubleshooting/inspection Service Points - How to Cope with Intermittent Malfunction ).