[Previous][Next]
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 sets DTC 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.
  • 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 (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 MB991958, diagnose the CAN bus line.
(1)
cautionTo prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
Connect scan tool MB991958. Refer to "How to connect the Scan Tool MB991958 ."
(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
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 MB991958, read the ASC-ECU diagnostic trouble code.
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 MB991958, read the ETACS diagnostic trouble code.
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 diagnostic trouble code.
Check again if the DTC is set in the SRS-ECU.
(1) Erase the DTC.
(2) Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3) Check if DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
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 diagnostic trouble code.
Check again if the DTC is set in the SRS-ECU.
(1) Erase the DTC.
(2) Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3) Check if DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
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 diagnostic trouble code.
Check again if the DTC is set in the SRS-ECU.
(1) Erase the DTC.
(2) Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3) Check if DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC set?
Return to Step 1.
The procedure is complete.