If diagnosis
code No. U0121 is set to the ETACS-ECU, always diagnose the CAN bus line.
Before replacing the ECU, ensure that the communication circuit is normal.
DIAGNOSTIC FUNCTION
If the signal from ASC-ECU cannot be received, the ETACS-ECU sets the diagnosis code No.
U0121.
JUDGMENT CRITERIA
After the following statuses continue to be true for 5 seconds, if the communication with
the ASC-ECU cannot be established for 600 ms or more, the ETACS-ECU determines that a problem
has occurred.
No abnormality is present to the network.
Ignition switch is in the ON position.
No abnormality is present to the power supply fuse, or the odometer value is at
80.5 km or more.
ETACS-ECU system voltage is at 10-16 V.
PROBABLE CAUSES
Malfunction of ASC-ECU
Malfunction of the ETACS-ECU
Malfunction of the CAN bus
DIAGNOSIS PROCEDURE
STEP 1. M.U.T.-III CAN bus diagnostics
Use the 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 -
Troubleshooting ).
STEP 2. M.U.T.-III other system diagnosis code
Check if diagnosis code is set to the ASC-ECU.
Q.
Is the diagnosis code set?
Troubleshoot the ASC (Refer to GROUP 35C -
Troubleshooting ).
Go to Step 3.
STEP 3. M.U.T.-III other system diagnosis code
Check if the diagnosis code No. U0121 is set to the engine ECU or 4WD-ECU.
Q.
Is the diagnosis code set?
Go to Step 4.
Go to Step 5.
STEP 4. Check whether the diagnosis code is reset.
Check again if the diagnosis code is set to the ETACS-ECU.
(1)Erase the diagnosis code.
(2)Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3)Check if diagnosis code is set.
Q.
Is the diagnosis code set?
Replace the ASC-ECU.
The trouble can be an intermittent malfunction such as a poor connection or open
circuit in the CAN bus lines between the ASC-ECU and the ETACS-ECU (GROUP 00 -
How
to use Troubleshooting/inspection Service Points -
How to Cope with Intermittent
Malfunction ).
STEP 5. Check whether the diagnosis code is reset.
Check again if the diagnosis code is set to the ETACS-ECU.
(1)Erase the diagnosis code.
(2)Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3)Check if diagnosis code is set.
Q.
Is the diagnosis code set?
Replace the ETACS-ECU.
The trouble can be an intermittent malfunction such as a poor connection or open
circuit in the CAN bus lines between the ASC-ECU and the ETACS-ECU (GROUP 00 -
How
to use Troubleshooting/inspection Service Points -
How to Cope with Intermittent
Malfunction ).
Repair the CAN bus line (Refer to GROUP 54C -
Troubleshooting 
).