If there is any problem in the CAN bus lines,
an incorrect diagnosis code may be set. Prior to this diagnosis, always diagnose the CAN bus
lines.
Before replacing the ECU, ensure that the communication circuit is normal.
OPERATION
4WD-ECU receives the data (such as ABS sensor signal, ABS operation signal) via the CAN
bus lines. If it cannot receive such data, it interrupts the system.
DIAGNOSIS CODE SET CONDITIONS
If the following conditions are met when the system is activated, 4WD-ECU gradually switches
the control from 4WD to 2WD, flashes the 4WD/LOCK indicators alternately, and sets
the diagnosis code No. U0121.
IG1 voltage: 10 V or more
ABS signal (such as wheel speed signal) cannot be received.
PROBABLE CAUSES
Current trouble
Wiring harness or connector failure between ASC-ECU and the stop lamp switch
Malfunction of the ABS sensor
Malfunction of the stop lamp switch
ASC-ECU malfunction
4WD-ECU malfunction
Past trouble
Refer to "How to treat past trouble" (GROUP 00 -
How to Treat Past Trouble )
for proceeding the diagnostics.
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 -
Troubleshooting .)
Then go to Step 2.
STEP 2. M.U.T.-III data list
Check the following service data. (Refer to .)
Item 07: CAN system (ABS/ASC)
Q.
Is the check result normal?
Go to Step 3.
Troubleshoot the ABS system. (Refer to GROUP 35C -
Troubleshooting .)
STEP 3. Check the following connector:
Check the connectors below for improper engagement, terminal damage or terminal drawn
in the connector case.
C-130 4WD-ECU connector
C-313, C-317 ETACS-ECU connector
Q.
Are the connectors and terminals in good condition?
Go to Step 4.
Repair the connector(s) or terminal(s). Then go to Step 6.
STEP 4. Wiring harness check
Check the wiring harness between the C-130 4WD-ECU connector and the C-313 ETACS-ECU connector
for damage or other problem.
Q.
Is the wiring harness in good condition?
Go to Step 5.
Repair damage or other problem in the wiring harness. Then go to Step 6.
STEP 5. Check whether the diagnosis code is reset.
(1)Erase the diagnosis code.
(2)Turn the ignition switch from the LOCK (OFF) position to the ON position.
(3)Check if the diagnosis code is set.
Q.
Is the diagnosis code No. U0121 set?
Replace 4WD-ECU. (Refer to .) Then go to Step
6.
This diagnosis is complete.
STEP 6. Check whether the diagnosis code is reset.
)
)
)
for proceeding the diagnostics.
Go to Step 2.
Repair the CAN bus line. (Refer to GROUP 54C -
Troubleshooting