If diagnosis
code No. U0121 is set to the ETACS-ECU, always diagnose the CAN bus line.
Before replacing the ECU, ensure that the power supply circuit, the earth circuit
and the communication circuit are normal.
When the ETACS-ECU of vehicles without KOS is replaced, the encrypted code of the ignition
key needs to be registered to the ETACS-ECU. (If the encrypted code is not registered, the engine
cannot be started. Register the encrypted code as described in Immobilizer System - How
to Register Key ID .)
DIAGNOSTIC FUNCTION
If the signal from ABS-ECU <vehicles without ASC> or ASC-ECU <vehicles
with ASC> cannot be received, the ETACS-ECU sets the diagnosis code No. U0121.
JUDGEMENT CRITERIA
After the following statuses continue to be true for 5 seconds, if the communication with
the ABS-ECU <vehicles without ASC> or ASC-ECU <vehicles with ASC> 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 (IOD 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 ABS-ECU <vehicles without ASC>
Malfunction of ASC-ECU <vehicles with ASC>
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 ABS-ECU <vehicles without ASC> or
ASC-ECU <vehicles with ASC>.
Q.
Is the diagnosis code set?
Set to the ABS-ECU. : Troubleshoot the ABS. Refer to GROUP 35B - Troubleshooting .
Set to the ASC-ECU. : Troubleshoot the ASC. Refer to GROUP 35C - Troubleshooting .
The diagnosis code is not set. : 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 ABS-ECU <vehicles without ASC> or ASC-ECU <vehicles
with ASC>.
The trouble can be an intermittent malfunction such as a poor connection or open
circuit in the CAN bus lines between the ABS-ECU <vehicles without ASC> or ASC-ECU <vehicles
with ASC> 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 ABS-ECU <vehicles without ASC> or ASC-ECU <vehicles
with ASC> 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 