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DTC U0121: CAN Time-out Error (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
TCM cannot receive the periodic communication data from the ASC-ECU.
 
 
MONITOR EXECUTION
Continuous
 
 
MONITOR EXECUTION CONDITIONS (OTHER MONITOR AND SENSOR)
Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
  • Not applicable
Sensor (The sensor below is determined to be normal)
  • Not applicable
 
 
LOGIC FLOW CHARTS (Monitor Sequence)
 
 
DTC SET CONDITIONS
Check Conditions
  • Time after TCM start: more than 0.7 second.
  • Voltage of battery: 10 volts or more
  • Voltage of battery: 16.5 volts or less
Judgment Criteria
  • No information is received from the ASC-ECU for 2.5 second.
 
 
OBD-II DRIVE CYCLE PATTERN
Ignition switch: "ON" position (start the engine and keep it for 10 seconds or more)
 
 
PROBABLE CAUSES
  • Malfunction of the CAN bus line
  • Malfunction of the hydraulic unit (integrated with ASC-ECU)
  • Malfunction of TCM
 
 
DIAGNOSIS
Required Special Tools:
  • MB992744: Vehicle communication interface-Lite (V.C.I.-Lite)
  • MB992745: V.C.I.-Lite main harness A
  • MB992747: V.C.I.-Lite USB cable short
  • MB992748: V.C.I.-Lite USB cable long
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)
    • MB991824: Vehicles Communication Interface (V.C.I.)
    • MB991827: M.U.T.-III USB Cable
    • MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)
caution
  • If the TCM is stored the DTC U0121, make sure to diagnose the CAN bus line.
  • If there is any problem in the CAN bus lines, an incorrect DTC may be stored. Prior to this diagnosis, diagnose the CAN bus lines.
  • Before replacing the ECU, ensure that the CAN bus line is normal.
STEP 1. Using scan tool (M.U.T.-III), diagnose the CAN bus lines.
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).
Using scan tool (M.U.T.-III), perform CAN bus diagnosis [Refer to GROUP 54C, Explanation About The Scan Tool (M.U.T.-III) Can Bus Diagnostics ].
Is the check result normal?
Go to Step 3.
Repair the CAN bus lines (Refer to GROUP 54C, Diagnosis - Can Bus Diagnostic Table ). Then go to Step 2.
 
STEP 2. Using scan tool (M.U.T.-III), DTC recheck after repairing CAN bus lines.
Check again if the DTC is stored.
(1) Erase the DTC.
(2) Turn the ignition switch to the "LOCK" (OFF) position.
(3) Carry out a test drive with the OBD-II drive cycle pattern.
(4) Recheck the DTC.
Is DTC U0121 stored?
Go to Step 3.
This diagnosis is complete.
 
STEP 3. Using scan tool (M.U.T.-III), check the DTC of other system.
Using scan tool (M.U.T.-III), check if the DTC is stored in ASC-ECU (Refer to GROUP 35C, Diagnosis - Diagnostic Function - How to Read and Erase Diagnostic Trouble Codes ).
Is any DTC stored?
Perform the ASC system diagnosis (Refer to GROUP 35C, Diagnosis - Diagnostic Trouble Code Chart ). Then go to Step 4
Go to Step 4.
 
STEP 4. Using scan tool (M.U.T.-III), check the DTC of other system.
Using scan tool (M.U.T.-III), check whether an ASC "time-out" related DTC is stored in other ECU (ECM, ETACS-ECU, combination meter, etc.).
Is any DTC stored?
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to GROUP 35C, Hydraulic Unit ). Then go to Step 6
Go to Step 5.
 
STEP 5. Using scan tool (M.U.T.-III), recheck the DTC.
Check again if the DTC is stored.
(1) Erase the DTC.
(2) Turn the ignition switch to the "LOCK" (OFF) position.
(3) Carry out a test drive with the OBD-II drive cycle pattern.
(4) Recheck the DTC.
Is DTC U0121 stored?
Replace the TCM (Refer to ). Then go to Step 6
The trouble can be an intermittent malfunction (Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
 
STEP 6. Using scan tool (M.U.T.-III), recheck the DTC.
Check again if the DTC is stored.
(1) Erase the DTC.
(2) Turn the ignition switch to the "LOCK" (OFF) position.
(3) Carry out a test drive with the OBD-II drive cycle pattern.
(4) Recheck the DTC.
Is DTC U0121 stored?
Return to Step 1.
This diagnosis is complete.