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Pinpoint Test C: U0121:87

WARNING: This page is about a different car, the 2021 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.
  1. Refer to MODULE COMMUNICATIONS NETWORK for schematic and connector information.

    Normal Operation and Fault Conditions 

    REFER to: Module Controlled Functions - System Operation and Component Description .

    DTC Fault Trigger Conditions 

    DTC Description Fault Trigger Condition
    BCM U0121:87 Lost Communication With Anti-Lock Brake System (ABS) Control Module "A": Missing Message A continuous memory DTC that sets in the BCMC if data messages received from the ABS module are missing.

    Possible Sources 

    • Communication network concern
    • Battery voltage concern
    • ABS module
    • BCMC (BJB)

  2. NOTE: If new modules were installed prior to the DTC being set, the module configuration may be incorrectly set during the PMI or the PMI may not have been carried out.

  3. C1 CHECK THE COMMUNICATION NETWORK

    • Ignition ON.

    • Connect the diagnostic tool.

    • Using a diagnostic scan tool, perform a network test.

    Does the ABS module pass the network test? 

    Yes  GO to C2 
    No  REFER to: Module Controlled Functions - System Operation and Component Description .

  4. C2 RECHECK THE BCMC (BODY CONTROL MODULE C) CONTINUOUS MEMORY DIAGNOSTIC TROUBLE CODES (CMDTCS)

    • Using a diagnostic scan tool, clear the Diagnostic Trouble Codes (DTCs).

    • Wait 10 seconds.

    • Using a diagnostic scan tool, check the BCMC Continuous Memory Diagnostic Trouble Codes (CMDTCs).

    Is DTC U0121:87 retrieved again? 

    Yes  GO to C3 
    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.

  5. C3 RETRIEVE THE ABS (ANTI-LOCK BRAKE SYSTEM) MODULE DTCS

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

    Are any ABS module DTCs present? 

    Yes  REFER to: Anti-Lock Brake System (ABS) and Stability Control .
    No  GO to C4 

  6. C4 RETRIEVE THE BCMC (BODY CONTROL MODULE C) DIAGNOSTIC TROUBLE CODES (DTCS)

    • Using a diagnostic scan tool, perform the BCMC self-test.

    Are any Diagnostic Trouble Codes (DTCs) recorded? 

    Yes  REFER to the BCMC DTC Chart.
    No  GO to C5 

  7. C5 CHECK FOR DTC (DIAGNOSTIC TROUBLE CODE) U0121:87 SET IN OTHER MODULES

    • Using a diagnostic scan tool, clear the DTCs.

    • Ignition OFF.

    • Wait 10 seconds.

    • Ignition ON.

    • Using a diagnostic scan tool, retrieve all  CMDTCs.

    Is DTC U0121:87 set in other modules? 

    Yes  GO to C6 
    No  GO to  C7

  8. C6 CHECK FOR CORRECT ABS (ANTI-LOCK BRAKE SYSTEM) MODULE OPERATION

    • Ignition OFF.

    • Disconnect and inspect the ABS 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 determine if the concern is still present.

    Is the concern still present? 

    Yes  CHECK OASIS for any applicable service articles: TSB, GSB, SSM or FSA. If a service article exists for this concern, DISCONTINUE this test and FOLLOW the service article instructions. If no service articles address this concern, INSTALL a new ABS module. REFER to: Anti-Lock Brake System (ABS) Module .
    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. C7 CHECK FOR CORRECT BCMC (BODY CONTROL MODULE C) OPERATION

    • Disconnect and inspect all BCMC 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 all BCMC connectors. Make sure they seat and latch correctly.

    • Operate the system and determine if the concern is still present.

    Is the concern still present? 

    Yes  CHECK OASIS for any applicable service articles: TSB, GSB, SSM or FSA. If a service article exists for this concern, DISCONTINUE this test and FOLLOW the service article instructions. If no service articles address this concern, INSTALL a new BCMC. REFER to: Body Control Module C (BCMC) .
    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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