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DTC U0121: CAN time-out error (ABS/ASC)
 
 
 
 
DIAGNOSTIC FUNCTION
The TCM determines that the system is defective if the TCM can receive no CAN communication information from the ASC-ECU.
 
 
DESCRIPTIONS OF MONITOR METHODS
No information is received from the ASC-ECU for 0.5 seconds.
 
 
MONITOR EXECUTION
  • When 1.05 seconds have elapsed after TCM started
 
 
MONITOR EXECUTION CONDITIONS (OTHER MONITOR AND SENSOR)
Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
  • P0712, P0713: Malfunction of the transmission fluid temperature sensor
  • P0715: Malfunction of primary pulley speed sensor
  • P0720: Malfunction of secondary pulley speed sensor
  • P0730: Incorrect gear ratio
  • P0966, P0967: Malfunction of secondary pressure solenoid valve
  • P0970, P0971: Malfunction of primary pressure solenoid valve
  • P2720, P2721: Malfunction of select pressure solenoid valve
  • P2763, P2764: Malfunction of lock-up solenoid valve
  • P2765: Malfunction of turbine speed sensor
Sensor (The sensor below is determined to be normal)
  • Transmission fluid temperature sensor
  • Primary pulley speed sensor
  • Secondary pulley speed sensor
  • Turbine speed sensor
 
 
LOGIC FLOW CHARTS (Monitor Sequence)
 
 
DTC SET CONDITIONS
Check Conditions
  • Voltage of battery: 10 volts or more
  • Time after TCM start: More than 1.05 seconds.
Judgment Criteria
  • CAN communication with ASC-ECU: fail. (0.5 second)
 
 
OBD-II DRIVE CYCLE PATTERN
Ignition switch: ON (start the engine and keep it for 10 seconds or more)
 
 
PROBABLE CAUSES
  • Malfunction of the CAN bus line
  • Malfunction of ASC-ECU
  • Malfunction of TCM
 
 
DIAGNOSIS
STEP 1. M.U.T.-III CAN bus diagnostics
Use scan tool to perform the CAN bus diagnosis.
Is the check result normal?
Go to Step 2.
Repair the CAN bus lines (Refer to GROUP 54C - Diagnosis, CAN Bus Diagnostics Table ).
 
STEP 2. M.U.T.-III diagnostic trouble code
Check if the ASC-related diagnostic trouble code is set.
Is the ASC-related diagnostic trouble code set?
Carry out the appropriate troubleshooting.
Go to Step 3.
 
STEP 3. M.U.T.-III diagnostic trouble code
Is diagnostic trouble code No. U0121 set in the other ECU, which communicates with the ASC-ECU via CAN?
Is the diagnostic trouble code set?
Go to Step 4.
Go to Step 5.
 
STEP 4. Symptom recheck after erasing diagnostic trouble code
Is the diagnostic trouble code set?
Replace ASC-ECU.
Intermittent malfunction.
 
STEP 5. Symptom recheck after erasing diagnostic trouble code
Is the diagnostic trouble code set?
Replace TCM.
Intermittent malfunction.