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Home >> Ford >> 2022 >> Mustang Mach 1 Premium, Automatic Trans >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 22 (Automatic Transmission - 7-Speed Automatic Transmission - Tr9070 (Diagnosis And Testing, General Procedures, Removal And Installation)) >> Diagnosis And Testing >> DTC Chart and Pinpoint Tests >> Pinpoint Tests >> Pinpoint Test R: DTC U0121

Pinpoint Test R: DTC U0121

WARNING: This page is about a different variant/trim than selected.
  1. Refer to MODULE COMMUNICATIONS NETWORK for schematic and connector information.

    Normal Operation and Fault Conditions 

    The TCM and the ABS module communicate through messages sent on HS-CAN. The TCM is on HS-CAN1 and the ABS module is on HS-CAN2, which communicate through GWM.

    DTC Fault Trigger Conditions 

    DTC Description Fault Trigger Condition
    TCM U0121:00 Lost Communication With Anti-Lock Brake System (ABS) Control Module 'A': No Sub Type Information The TCM sets this DTC if data messages received from the ABS module over the HS-CAN are missing for longer than 5 seconds.

    Possible Sources 

    • Communication concern
    • Battery voltage concern
    • ABS module
    • TCM

  2. R1 VERIFY THE SCAN TOOL COMMUNICATES WITH THE ABS (ANTI-LOCK BRAKE SYSTEM) MODULE

    • Using a diagnostic scan tool, carry out the ABS module self-test.

    Did the ABS module complete the self-test? 

    Yes  GO to  R2
    No  To diagnose the ABS module does not communicate with the scan tool, REFER to: Communications Network

  3. R2 CHECK THE TCM (TRANSMISSION CONTROL MODULE) FOR DIAGNOSTIC TROUBLE CODES (DTCS)

    • Using a diagnostic scan tool, clear all diagnostic trouble codes (DTCs) from the TCM.

    • Road test the vehicle.

    • Using a diagnostic scan tool, carry out the TCM self-test.

    Is DTC U0121 still present? 

    Yes  If diagnostic trouble codes (DTCs) U0103, U0115, U0140 and U0155 are all also present, indicating the HS-CAN bus is down, GO to Pinpoint Test U  Otherwise, GO to  R3
    No  The system is operating correctly at this time. The DTC may have been set due to high network traffic or an intermittent fault condition.

  4. R3 RETRIEVE ALL DIAGNOSTIC TROUBLE CODES (DTCS) FROM THE ABS (ANTI-LOCK BRAKE SYSTEM) MODULE SELF-TEST

    • Using a diagnostic scan tool, retrieve all diagnostic trouble codes (DTCs) from the ABS module self-test.

    Are any diagnostic trouble codes (DTCs) present in the ABS module? 

    Yes  RESOLVE all ABS module diagnostic trouble codes (DTCs) first. REFER to: Anti-Lock Brake System (ABS) and Stability Control
    No  GO to  R4

  5. R4 RETRIEVE ALL DIAGNOSTIC TROUBLE CODES (DTCS) FROM THE TCM (TRANSMISSION CONTROL MODULE) SELF-TEST

    • Using a diagnostic scan tool, retrieve all diagnostic trouble codes (DTCs) from the TCM self-test.

    Is DTC P0882 or P0883 recorded? 

    Yes  RESOLVE those diagnostic trouble codes (DTCs) first. REFER to the Diagnostic Trouble Code (DTC) Chart .
    No  GO to  R5

  6. R5 CHECK GWM (GATEWAY MODULE A) FOR DIAGNOSTIC TROUBLE CODES (DTCS)

    • Using a diagnostic scan tool, carry out the GWM self-test.

    Are any diagnostic trouble codes (DTCs) present in GWM? 

    Yes  RESOLVE those diagnostic trouble codes (DTCs) first. REFER to: Communications Network
    No  GO to  R6

  7. R6 CHECK FOR DTC (DIAGNOSTIC TROUBLE CODE) U0121 SET IN OTHER MODULES

    • Using a diagnostic scan tool, retrieve all continuous memory diagnostic trouble codes (CMDTCs) from all modules.

    Is DTC U0121 set in other modules on the network? 

    Yes  GO to  R7
    No  GO to  R8

  8. R7 CHECK FOR CORRECT ABS (ANTI-LOCK BRAKE SYSTEM) MODULE OPERATION

    • Ignition OFF.

    • Disconnect and inspect the ABS module connector.

    • Repair:

      • corrosion (install new connector or terminals - clean module pins)
      • damaged or bent pins - install new terminals/pins
      • pushed-out pins - install new pins as necessary

    • Reconnect the ABS module connector. Make sure it seats and latches correctly.

    • Operate the system and verify the concern is still present

    Is the concern still present? 

    Yes  CHECK OASIS for any applicable TSBs. If a TSB exists for this concern, DISCONTINUE this test and FOLLOW TSB instructions. If no TSBs address this concern, INSTALL a new ABS. Refer to ABS Guided Routine Testing .
    No  The system is operating correctly at this time. The concern may have been caused by module connections. ADDRESS the root cause of any connector or pin issues.

  9. R8 CHECK FOR CORRECT TCM (TRANSMISSION CONTROL MODULE) OPERATION

    • Ignition OFF.

    • Disconnect and inspect the TCM connectors.

    • Repair:

      • corrosion (install new connector or terminals - clean module pins)
      • damaged or bent pins - install new terminals/pins
      • pushed-out pins - install new pins as necessary

    • Reconnect the TCM connectors. Make sure they seat and latch correctly.

    • Operate the system and verify the concern is still present

    Is the concern still present? 

    Yes  CHECK OASIS for any applicable TSBs. If a TSB exists for this concern, DISCONTINUE this test and FOLLOW TSB instructions. If no TSBs address this concern, INSTALL a new TCM. REFER to: Transmission Control Module (TCM) 
    No  The system is operating correctly at this time. The concern may have been caused by module connections. ADDRESS the root cause of any connector or pin issues.
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