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Pinpoint Test C: U0121:87

WARNING: This page is about a different car, the 2023 Ford Bronco. However, it is still accessible from the selected car via links, so may be relevant.
  1. Refer to MODULE COMMUNICATION NETWORK for schematic and connector information.

    Normal Operation and Fault Conditions 

    REFER to: Controller Area Network (CAN) Module Communications Network - 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 BCM if messages from the ABS module over the FD-CAN through the GWM on the HS-CAN to the BCM are missing.

    Possible Sources 

    • Communication network concern
    • Battery voltage concern
    • ABS module
    • GWM
    • BCM

    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.

  2. C1 CHECK THE COMMUNICATION NETWORK

    • Connect the diagnostic tool.

    • Ignition ON.

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

    Does the ABS module pass the network test? 

    Yes  GO to C2 
    No  REFER to: Controller Area Network (CAN) Module Communications Network .

  3. C2 CHECK THE BCM (BODY CONTROL MODULE) 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 BCM CMDTCs.

    Are BCM voltage DTCs recorded? 

    Yes  For voltage below threshold DTCs, GO to Pinpoint Test V  For voltage above threshold DTCs, GO to Pinpoint Test X 
    No  GO to C3 

  4. C3 RETRIEVE THE ABS (ANTI-LOCK BRAKE SYSTEM) MODULE DTCS FROM THE SELF-TEST

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

    Are any ABS related DTCs present? 

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

  5. C4 RECHECK THE BCM (BODY CONTROL MODULE) CMDTCS

    • Using a diagnostic scan tool, clear the DTCs.

    • Wait 10 seconds.

    • Using a diagnostic scan tool, check the BCM CMDTCs.

    Is DTC U0121:87 still present? 

    Yes  GO to C5 
    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.

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

    • Using a diagnostic scan tool, clear the DTCs.

    • Ignition OFF.

    • Ignition ON.

    • Wait 10 seconds.

    • Using a diagnostic scan tool, retrieve all CMDTCs.

    Is DTC U0121:87 set in other modules? 

    Yes  GO to C6 
    No  GO to C7 

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

    • 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 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 - Vehicles With: Vacuum Brake Booster .
    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.

  8. C7 CHECK FOR CORRECT BCM (BODY CONTROL MODULE) OPERATION

    • Disconnect and inspect all BCM 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 BCM 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 BCM. REFER to: Body Control Module (BCM) .
    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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