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DTC U0121: ABS/ASC CAN timeout
 
 
caution
  • If DTC U0121 is set in the SRS-ECU, diagnose the CAN bus line.
  • Whenever the ECU is replaced, ensure that the communication circuit is normal.
 
 
DIAGNOSTIC FUNCTION
If the signal from ASC-ECU cannot be received, the SRS-ECU stores the 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 0.6 second or more, the SRS-ECU determines that a problem has occurred.
  • No abnormality is present to the network.
  • Electric motor 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 (50.0 miles) or more.
  • SRS-ECU system voltage is at 10-16 volts.
 
 
TROUBLESHOOTING HINTS
  • The ASC-ECU may be defective.
  • The SRS-ECU may be defective.
  • The CAN bus may be defective.
 
 
DIAGNOSIS
STEP 1. Using scan tool (M.U.T.-IIISE), diagnose the CAN bus line.
(1)
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn off the power supply mode of the electric motor switch before connecting or disconnecting scan tool (M.U.T.-IIISE).
Connect scan tool (M.U.T.-IIISE). Refer to "How to connect the Scan Tool ."
(2) Turn on the power supply mode of the electric motor switch.
(3) Diagnose the CAN bus line.
(4) Turn off the power supply mode of the electric motor switch.
Is the CAN bus line found to be normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C, Diagnosis ). On completion, go to Step 6.
 
STEP 2. Using scan tool (M.U.T.-IIISE), read the ASC-ECU DTC.
Check if DTC is set in the ASC-ECU.
Is the DTC set?
Troubleshoot the ASC-ECU (Refer to GROUP 35C, Diagnosis ). On completion, go to Step 6.
Go to Step 3.
 
STEP 3. Using scan tool (M.U.T.-IIISE), read the ETACS DTC.
Check if DTC U0121 is set in the ETACS-ECU.
Is the DTC set?
Go to Step 4.
Go to Step 5.
 
STEP 4. Recheck for DTC.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn on the power supply mode of the electric motor switch.
(3) Check if the DTC is set.
(4) Turn off the power supply mode of the electric motor switch.
Is the DTC set?
Replace the ASC-ECU. Then, carry out the CAN bus diagnostics. Then go to Step 6.
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 SRS-ECU (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).
 
STEP 5. Recheck for DTC.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn on the power supply mode of the electric motor switch.
(3) Check if the DTC is set.
(4) Turn off the power supply mode of the electric motor switch.
Is the DTC set?
Replace the SRS-ECU. Then, carry out the CAN bus diagnostics. Then go to Step 6.
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 SRS-ECU (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).
 
STEP 6. Recheck for DTC.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn on the power supply mode of the electric motor switch.
(3) Check if the DTC is set.
(4) Turn off the power supply mode of the electric motor switch.
Is the DTC set?
Return to Step 1.
The procedure is complete.