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

caution

If diagnosis code No. U0121 is set in the engine-ECU, surely perform CAN bus line diagnosis.
Replace ECU after certainly confirming that the communication circuits are normal.

TROUBLE JUDGEMENT

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 16.5 V.

Judgement Criterion

Unable to receive ASC-ECU 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 ASC-ECU, by malfunction in the power supply system of ASC-ECU, in ASC-ECU 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 ASC-ECU and malfunction in the power supply system of ASC-ECU. 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 ASC-ECU
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 Diagnosis Table ). After repairing CAN bus line, go to Step 6.

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

Confirm whether the diagnosis code is set in the ASC-ECU.

Q. Is diagnosis code set?

	Perform troubleshooting of the ASC system (Refer to GROUP 35C - Troubleshooting, Diagnosis Code Chart ).

	Go to Step 3.

STEP 3. 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-related Diagnosis Code Table

Q. Is diagnosis code No. U0121 set?

	Go to Step 4.

	Go to Step 5.

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

Confirm again whether the diagnosis code is set in the engine-ECU.

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

Q. Is diagnosis code No. U0121 set?

	After replace the hydraulic unit assembly (integrated with ASC-ECU) (Refer to GROUP 35C - Hydraulic Unit ). Then go to Step 6.

	Intermittent malfunction in CAN bus line between engine-ECU and ASC-ECU (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.

Confirm again whether the diagnosis code is set in the engine-ECU.

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

Q. Is diagnosis code No. U0121 set?

	After replacing engine-ECU. Then go to Step 6.

	Intermittent malfunction in CAN bus line between engine-ECU and ASC-ECU (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.

Confirm again whether the diagnosis code is set in the engine-ECU.

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

Q. Is diagnosis code No. U0121 set?

	Go to Step 1.

	This diagnosis is complete.