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DTC U0121: ABS/ASC CAN timeout
 
 
caution
  • If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ).
  • If DTC U0121 is set in electric parking brake ECU, always diagnose the CAN bus line. If there is any fault in the CAN bus lines, an incorrect DTC may be set. In this case, the set DTC is not highly reliable.
  • Whenever ECU is replaced, ensure that the CAN bus lines are normal.
 
 
OPERATION
The electric parking brake ECU communicates with the ASC-ECU via the CAN bus lines.
 
 
DTC SET CONDITIONS
If the ECU cannot receive any signal from the ASC-ECU via CAN for 500 ms or more, this DTC will be set.
 
 
TROUBLESHOOTING HINTS
  • The CAN bus line is defective.
  • Power supply circuit for the ASC-ECU fails
  • Malfunction of the ASC-ECU
  • Malfunction of the electric parking brake ECU
 
 
DIAGNOSIS
STEP 1. Scan tool (M.U.T.-III) CAN bus diagnosis
(1)
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
Connect scan tool (M.U.T.-III). Refer to "How to connect the Scan Tool (M.U.T.-III) ."
(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 check result normal?
Go to Step 3.
Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ). On completion, go to Step 2.
 
STEP 2. DTC recheck after resetting CAN bus lines
Is DTC No. U0121 set?
Go to Step 3.
This diagnosis is complete.
 
STEP 3. Check for DTCs of other systems.
Check whether an ASC "time-out" related DTC is set in other ECUs (Refer to GROUP 54C - CAN-Related DTC Table ).
Is the DTC set?
Go to Step 4.
Go to Step 5.
 
STEP 4. Check whether the DTC is set again.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to the "LOCK" (OFF) position.
(3) Turn the ignition switch to the "ON" position.
(4) Check if the DTC is set.
Is DTC No. U0121 set?
Replace the hydraulic unit (ASC-ECU) (Refer to GROUP 35C - Hydraulic Unit ).
The trouble can be an intermittent malfunction (GROUP 00 - How to use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
 
STEP 5. Check whether the DTC is set again.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to the "LOCK" (OFF) position.
(3) Turn the ignition switch to the "ON" position.
(4) Check if the DTC is set.
Is DTC No. U0121 set?
Replace the electric parking brake ECU (Refer to ).
The trouble can be an intermittent malfunction (GROUP 00 - How to use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).