Code No.U1120: Engine malfunction detection

caution

If diagnosis code No.U1120 is set in the ASTC-ECU, always diagnose the CAN main bus line. If there is any fault in the CAN bus lines, an incorrect diagnosis code may be set.
Whenever the ECU is replaced, ensure that the communication circuit is normal.

DIAGNOSIS CODE SET CONDITION

The ASTC-ECU receives engine system-related signals from the Engine-ECU via CAN bus lines. If a fail-safe related data is contained in the signal from the Engine-ECU, diagnosis code No.U1120 will be stored.

PROBABLE CAUSES

Damaged harness or connector.
Malfunction of the Engine-ECU.
Malfunction of the ASTC-ECU.

DIAGNOSIS PROCEDURE

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

Use 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 - CAN Bus Diagnostics Table ). Then go to Step 5.

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

Check whether the diagnosis code No. U1120 is set by another ECU.

Q. Is the diagnosis code set?

	Replace the Engine-ECU (Refer to GROUP 13A - Engine-ECU ). Then go to Step 5.

	Go to Step 3.

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

Check whether the diagnosis code is set by the Engine-ECU.

Q. Is any diagnosis code set?

	Perform troubleshooting for Engine-ECU (Refer to GROUP 13A - Troubleshooting ). Then go to Step 5.

	Go to Step 4.

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

(1)Turn the ignition switch to the "ON" position.

(2)Erase the diagnosis code.

(3)Turn the ignition switch to the "LOCK" (OFF) position.

(4)Turn the ignition switch to the "ON" position.

(5)Check if the diagnosis code is set.

(6)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is code No.U1120 set?

	Replace the hydraulic unit (integrated with ASTC-ECU) (Refer to ). Then go to Step 5.

	Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).

STEP 5. Check whether the diagnosis code is reset.