Code No. U0121: ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> Time-out

caution

If diagnosis code U0121 is set from engine-ECU, surely perform CAN bus line diagnosis.

caution

Replace ECU after certainly confirming that the communication circuits are normal.

TROUBLE JUDGMENT

Check Conditions

More than 2 seconds have passed since the ignition switch was turned to "ON" position.
Battery positive voltage is more than 10 V and is less than 16 V.

Judgement Criterion

Unable to receive ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> signals through the CAN bus line for 4 seconds.

COMMENTS ON TROUBLE SYMPTOM

Current malfunction

The failure is possibly caused by malfunction of the harness and connector in CAN bus line between engine-ECU and ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>, by malfunction in the power supply system of ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>, in ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> itself, in engine-ECU.

Past malfunction

Proceed with troubleshooting focusing on malfunction of the harness and connector in CAN bus line between engine-ECU and ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> and malfunction in the power supply system of ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>.For diagnosis procedure, refer to how to cope with past malfunctions. (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Treat Past Trouble

note

In the case of past malfunctions, M.U.T.-III CAN bus line diagnosis cannot detect a malfunction even if there is a malfunction in CAN bus. Therefore, check CAN bus line as in the case of response to intermittent malfunctions (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions

). It is possible to narrow down areas with a high possibility of malfunctions from diagnosis codes set to each ECU that performs CAN communication (Refer to GROUP 54C - Explanation about the M.U.T.-III CAN Bus Diagnostics

FAIL-SAFE AND BACKUP FUNCTION

None

PROBABLE CAUSES

Failed harness and connector
Failed ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>
Failed engine-ECU

DIAGNOSIS PROCEDURE

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

Use M.U.T.-III to perform CAN bus line diagnosis.

Q. Is the check result normal?

	Go to Step 2.

	Repair CAN bus line (Refer to GROUP 54C - Troubleshooting - CAN Bus Diagnostics Table ). After repairing CAN bus line, go to Step 6 .

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

Confirm the diagnosis code is set from the ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>.

Q. Is diagnosis code set?

	Perform troubleshooting of the anti-lock brake system (ABS) or the active stability control (ASC) system (Refer to GROUP 35B - Troubleshooting <Vehicles with ABS>, Refer to GROUP 35C - Troubleshooting - Diagnosis Code Chart <Vehicles with ASC>).

	Go to Step 3.

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

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

Q. Is diagnosis code set?

	Go to Step 4.

	Go to Step 5.

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

Reconfirmation of diagnosis code.

Confirm again the diagnosis code is set from the engine-ECU.

Erase the set diagnosis code.
Ignition switch: "LOCK" (OFF) → "ON"
Confirm whether the diagnosis code is set.

Q. Is diagnosis code set?

	After replacing ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC>, go to Step 6.

	Intermittent malfunction in CAN bus line between engine-ECU and ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

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

Reconfirmation of diagnosis code.

Confirm again the diagnosis code is set from the engine-ECU.

Erase the set diagnosis code.
Ignition switch: "LOCK" (OFF) → "ON"
Confirm whether the diagnosis code is set.

Q. Is diagnosis code set?

	After replacing engine-ECU, go to Step 6.

	Intermittent malfunction in CAN bus line between engine-ECU and ABS-ECU <Vehicles with ABS> or ASC-ECU <Vehicles with ASC> (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

STEP 6. M.U.T.-III diagnosis code

Reconfirmation of diagnosis code.

Confirm again the diagnosis code is set from the engine-ECU.

Erase the set diagnosis code.
Ignition switch: "LOCK" (OFF) → "ON"
Confirm whether the diagnosis code is set.

Q. Is diagnosis code set?

	Go to Step 1.

	Check end.