If diagnosis code U1073 is set in the A/T-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 CONDITIONS
The failure is possibly caused by malfunction of the harness and connector in CAN busline
or by malfunction in A/T-ECU.
PROBABLE CAUSES
Damaged wiring harness or connector
Malfunction of the A/T-ECU
DIAGNOSIS PROCEDURE
STEP 1. M.U.T.-III CAN bus diagnostics
Using M.U.T.-III, perform CAN busline diagnosis.
Q.
Is the check result normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C, CAN bus line Diagnostic flow .)
Then go to Step 3.
STEP 2. M.U.T.-III diagnosis code
Check again if the diagnosis code is set.
(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.U1073 set?
Replace the A/T-ECU. Then go to Step 3.
Intermittent malfunction (Refer to GROUP 00 -
How to Use Troubleshooting/Inspection
Service Points ).
STEP 3. Check whether the diagnosis code is reset.
Check again if the diagnosis code is set.
(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.
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C, CAN bus line Diagnostic flow 
.)
Then go to Step 3.