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



DIAGNOSIS

STEP 1. M.U.T.-III other system diagnosis code


(1)
caution To prevent damage to M.U.T.-III, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting M.U.T.-III.
Connect the M.U.T.-III to the diagnosis connector as shown in the illustration.
(2)Turn the ignition switch to the "ON" position.
(3)Check for MPI system diagnosis code (Refer to GROUP 13A, Diagnosis Function .)
(4)Turn the ignition switch to the "LOCK" (OFF) position.
(5)Disconnect M.U.T.-III.

Q. Is any diagnosis code set?

Repair the MPI control system. (Refer to GROUP 13A, Diagnosis Function .) Then go to Step 5.

Go to Step 2.

STEP 2. M.U.T.-III CAN bus diagnostics


caution To prevent damage to M.U.T.-III, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting M.U.T.-III.
(1)Connect the M.U.T.-III to the diagnosis connector as shown in the illustration.
(2)Turn the ignition switch to the "ON" position.
(3)Diagnose the CAN bus line. (Refer to GROUP 54C, CAN bus line Diagnostic flow .)
(4)Turn the ignition switch to the "LOCK" (OFF) position.
(5)Disconnect M.U.T.-III.

Q. Is the check result normal?

Go to Step 3.

Repair the CAN bus line (Refer to GROUP 54C, CAN bus line Diagnostic flow .) Then go to Step 5.

STEP 3. Check whether the diagnosis code is reset.


(1)
caution To prevent damage to M.U.T.-III, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting M.U.T.-III.
Connect the M.U.T.-III to the diagnosis connector as shown in the illustration.
(2)Turn the ignition switch to the "ON" position.
(3)Erase the diagnosis code (Refer to .)
(4)Turn the ignition switch to the "LOCK" (OFF) position.
(5)Turn the ignition switch to the "ON" position.
(6)Check if the diagnosis code is set.
(7)Turn the ignition switch to the "LOCK" (OFF) position.
(8)Disconnect M.U.T.-III.

Q. Is code No.U1120 set?

Replace the hydraulic unit (integrated with ASTC-ECU.) Then go to Step 4.

It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction .

STEP 4. Check whether the diagnosis code is reset.
Check again if the diagnosis code is set.


(1)
caution To prevent damage to M.U.T.-III, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting M.U.T.-III.
Connect the M.U.T.-III to the diagnosis connector as shown in the illustration.
(2)Turn the ignition switch to the "ON" position.
(3)Erase the diagnosis code (Refer to .)
(4)Turn the ignition switch to the "LOCK" (OFF) position.
(5)Turn the ignition switch to the "ON" position.
(6)Check if the diagnosis code is set.
(7)Turn the ignition switch to the "LOCK" (OFF) position.
(8)Disconnect M.U.T.-III.

Q. Is code No.U1120 set?

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

It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction .

STEP 5. Check whether the diagnosis code is reset.


(1)
caution To prevent damage to M.U.T.-III, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting M.U.T.-III.
Connect the M.U.T.-III to the diagnosis connector as shown in the illustration.
(2)Turn the ignition switch to the "ON" position.
(3)Erase the diagnosis code (Refer to .)
(4)Turn the ignition switch to the "LOCK" (OFF) position.
(5)Turn the ignition switch to the "ON" position.
(6)Check if the diagnosis code is set.
(7)Turn the ignition switch to the "LOCK" (OFF) position.
(8)Disconnect M.U.T.-III.

Q. Is code No.U1120 set?

Return to Step 1.

The procedure is complete.