Code No.U0121 ABS/ASC CAN timeout


caution
  • If diagnosis code U0121 is set in the combination meter, always diagnose the CAN bus lines.
  • Whenever the ECU is replaced, ensure that the communication circuit is normal.

TROUBLE JUDGEMENT


The combination meter sets diagnosis code No.U0121 when it cannot receive signals from the ABS-ECU <Vehicles without ASTC> or ASTC-ECU <Vehicles with ASTC>.

JUDGEMENT CRITERIA


With the ignition switch is at ON position, diagnosis code No. U1190 is not set and diagnosis code No. U1195 is not set, if the communication with ABS-ECU or ASTC-ECU cannot be established for 2500 ms or more, the combination meter determines that a problem has occurred.

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 ).

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


Check that the ABS-ECU or ASTC-ECU sets a diagnosis code.

Q. Is the diagnosis code set?

Diagnose the ABS-ECU (Refer to GROUP 35B - Troubleshooting ) or ASTC-ECU (Refer to GROUP 35C - Troubleshooting ).

Go to Step 3.

STEP 3. M.U.T.-III other system diagnosis code


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 set again.


Check again if the diagnosis code is set in the combination meter.
(1)Erase the diagnosis code.
(2)Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3)On completion, check that the diagnosis code is set again.

Q. Is the diagnosis code set?

Replace the ABS-ECU (Refer to GROUP 35B - Hydraulic unit ) or ASTC-ECU (Refer to GROUP 35C - Hydraulic unit ) and then go to Step 6.

A poor connection, open circuit or other intermittent malfunction is present in the CAN bus lines between the ABS-ECU or ASTC-ECU and the combination meter (Refer to GROUP 00 - How to use troubleshooting/Inspection Service Points ).

STEP 5. Check whether the diagnosis code is set again.


Check again if the diagnosis code is set in the combination meter.
(1)Erase the diagnosis code.
(2)Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3)On completion, check that the diagnosis code is set again.

Q. Is the diagnosis code set?

Replace the combination meter (Refer to ) and then go to Step 6.

A poor connection, open circuit or other intermittent malfunction is present in the CAN bus lines between the ASC-ECU and the combination meter (Refer to GROUP 00 - How to use troubleshooting/Inspection Service Points ).

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


Recheck if the diagnosis code is set in the combination meter.
(1)Erase the diagnosis code.
(2)Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3)On completion, check that the diagnosis code is set again.

Q. Is the diagnosis code set?

Return to Step 1.

The procedure is complete.