Code No. U0121:
ABS/ASC CAN timeout
| caution |
- If diagnosis
code No. U0121 is set in the multivision display, always diagnose the CAN bus lines.
- Whenever the ECU is replaced, ensure that the communication circuit is normal.
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| note |
When the diagnosis codes relating to the CAN communication error are set, make sure of
the vehicle equipment. When the vehicle is not equipped with the system the multivision display communicates
to, the diagnosis code is always set. This is not abnormal.
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TROUBLE JUDGEMENT
The multivision display receives transmission control system-related signal from the ASTC-ECU
via CAN bus lines. If the display unit cannot receive the necessary signals, diagnosis code No. U0121
will be set.
COMMENTS ON TROUBLE SYMPTOM
Current trouble
- Connector(s) or wiring harness in the CAN bus lines between the ASTC-ECU and the
multivision display, the power supply system to the ASTC-ECU, the ASTC-ECU itself, or the multivision display
may be defective.
Past trouble
- Carry out diagnosis with particular emphasis on connector(s) or wiring harness in
the CAN bus lines between the ASTC-ECU and the multivision display, and the power supply system
to the ASTC-ECU. For diagnosis procedures, refer to "How to cope with past trouble" (Refer to
GROUP 00 - How to Use Troubleshooting/Inspection Service Points).
| note |
For a past trouble, you may not find it by the M.U.T.-III CAN bus diagnostics even if
there is any failure in CAN bus lines. In this case, refer to GROUP 00, How to Use Troubleshooting/Inspection
Service Points. and check the CAN bus lines. You can narrow down the possible cause of the trouble
by referring to the diagnosis code, which is set regarding the CAN communication-linked ECUs
(Refer to GROUP 54C - CAN Bus Line Diagnostic Flow).
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PROBABLE CAUSES
- Damaged harness wires and connectors
- Malfunction of ASTC-ECU
- Malfunction of multivision display
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 lines. (Refer to GROUP 54C - Troubleshooting 
).
Repair the CAN bus line and go to Step 6.
STEP 2. M.U.T.-III other system diagnosis code
Check whether the ASTC system diagnosis codes are set or not.
Q.
Is the diagnosis code set?
Diagnose the ASTC-ECU troubleshooting (GROUP 35C - Troubleshooting).
Go to Step 3.
STEP 3. M.U.T.-III other system diagnosis code
Check if a diagnosis code, which relates to CAN communication-linked systems below, is
set.
Combination meter
- Code No. U0121: ABS/ASC CAN timeout
Q.
Is the diagnosis code set?
Go to Step 4.
Go to Step 5.
STEP 4. Check whether the diagnosis code is set again.
Recheck if the diagnosis code is set.
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(1)Erase the diagnosis code.
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(2)Turn the ignition switch to "ON" position.
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(3)On completion, check that the diagnosis code is not set again.
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Q.
Is the diagnosis code set?
Replace hydraulic unit assembly (integrated with ASTC-ECU) and then go to Step
6.
A poor connection, open circuit or other intermittent malfunction is present in
the CAN bus lines between the ASTC-ECU and the multivision display (Refer to GROUP 00 - How
to use troubleshooting/Inspection Service Points).
STEP 5. Check whether the diagnosis code is set again.
Recheck if the diagnosis code is set.
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(1)Erase the diagnosis code.
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(2)Turn the ignition switch to "ON" position.
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(3)On completion, check that the diagnosis code is not set again.
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Q.
Is the diagnosis code set?
Replace multivision display (Refer to ) and then
go to Step 6.
A poor connection, open circuit or other intermittent malfunction is present in
the CAN bus lines between the ASTC-ECU and the multivision display (Refer to GROUP 00 - How
to Use Troubleshooting/Inspection Service Points).
STEP 6. Check whether the diagnosis code is set again.
Recheck if the diagnosis code is set.
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(1)Erase the diagnosis code.
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(2)Turn the ignition switch to "ON" position.
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(3)On completion, check that the diagnosis code is not set again.
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Q.
Is the diagnosis code set?
Go to Step 1.
The procedure is complete.