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DTC U0121 ABS/ASC CAN timeout
 
 
caution
  • If DTC U0121 is set in the BSW-ECU (master), always diagnose the CAN bus line.
  • Before replacing the ECU, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.
 
 
OPERATION
The BSW-ECU (master) communicates with the ASC-ECU via the gateway-ECU and CAN bus lines.
 
 
CHECK CONDITION
Ignition switch is in the "ON" position.
 
 
DIAGNOSTIC FUNCTION AND TROUBLE JUDGMENT
If the BSW-ECU (master) cannot receive any signal from the ASC-ECU for at least 2.5 seconds, the ECU sets DTC U0121.
 
 
TROUBLESHOOTING HINTS
  • Power supply to the ASC-ECU fails
  • Malfunction of the ASC-ECU
  • Power supply to the gateway-ECU fails
  • Malfunction of the gateway-ECU
  • Malfunction of the BSW-ECU (master)
  • Malfunction of the CAN bus
 
 
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 the ignition switch to the "LOCK" (OFF) position 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 (M.U.T.-IIISE) ."
(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 - Troubleshooting ).
 
STEP 2. Using scan tool (M.U.T.-IIISE), read the other system DTC.
Check that the other ECU performing CAN communication with ASC-ECU sets DTC U0121 [Refer to GROUP 54C - CAN Communication-related Diagnostic Trouble Code (U-code) Table ].
Is the DTC set?
Go to Step 3.
Go to Step 4.
 
STEP 3. Using scan tool (M.U.T.-IIISE), read the DTC again.
Check again if the DTC is set in the BSW-ECU (master).
(1) Erase the DTC.
(2) Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3) Check if DTC is set.
Is the DTC set?
Replace the ASC-ECU.
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 BSW-ECU (master) (Refer to GROUP 00 - How to use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
 
STEP 4. Using scan tool (M.U.T.-IIISE), read the other DTC.
Check if DTC U0146 is set.
Is the DTC set?
Follow DTC procedure No. U0146 (Refer to ).
Go to Step 5.
 
STEP 5. Using scan tool (M.U.T.-IIISE), read the other system DTC.
Check if DTC U1073 is set in the gateway-ECU.
Is the DTC set?
Troubleshoot the gateway-ECU (Refer to GROUP 54C - Troubleshoot <Gateway> - Diagnostic Trouble Code Chart ).
Go to Step 6.
 
STEP 6. Using scan tool (M.U.T.-IIISE), read the DTC again.
Check again if the DTC is set in the BSW-ECU (master).
(1) Erase the DTC.
(2) Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3) Check if DTC is set.
Is the DTC set?
Replace the BSW-ECU (master).
Intermittent malfunction is suspected (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).