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Pinpoint Test G : U0121:87

WARNING: This page is about a different car, the 2020 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.
  1. Refer to Vehicle Dynamic Systems for schematic and connector information.

    Normal Operation and Fault Conditions 

    With the ignition ON, the ABS module sends messages to the VDM over the HS-CAN2. If the VDM does not receive these messages within a certain time frame, the module sets Diagnostic Trouble Codes (DTCs). For information on the messages sent to the VDM by the ABS module, go to the Network Message Chart. REFER to: Vehicle Dynamic Suspension - System Operation and Component Description .

    DTC Fault Trigger Conditions 

    DTC Description Fault Trigger Condition
    VDM U0121:87 Lost Communication With Anti-Lock Brake System (ABS) Control Module "A": Missing Message This DTC sets in continuous memory if any one of the following messages is missing: ABS active, brake torque request, stability control mode, stability control indicator request, traction control mode, vehicle lateral acceleration, vehicle longitudinal acceleration, vehicle roll rate or vehicle vertical acceleration. This can be due to a ABS module failure, a circuit failure on the ABS module or an excessive load on the network.

    Possible Sources 

    • Wiring, terminals or connectors
    • Network communication concern
    • Vehicle battery
    • Charging system concern
    • ABS

  2. G1 CHECK THE COMMUNICATION NETWORK

    • Ignition ON.

    • Using a diagnostic scan tool, carry out the Network Test.

    Does the ABS module pass the Network Test? 

    Yes  GO to  G2
    No  DIAGNOSE the ABS module does not respond to the diagnostic scan tool. REFER to: Communications Network .

  3. G2 CHECK THE VDM (VEHICLE DYNAMICS CONTROL MODULE) DIAGNOSTIC TROUBLE CODES (DTCS)

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

    • Clear the Diagnostic Trouble Codes (DTCs).

    • Ignition OFF.

    • Open and Close drivers door.

    • Wait 2 1/2 minutes.

    • Ignition ON.

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

    • Record the VDM Diagnostic Trouble Codes (DTCs).

    Is DTC U0121:87 retrieved again? 

    Yes  GO to  G3
    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. G3 REVIEW THE RECORDED DIAGNOSTIC TROUBLE CODES (DTCS) FROM THE VDM (VEHICLE DYNAMICS CONTROL MODULE) SELF-TEST

    • Check the recorded Diagnostic Trouble Codes (DTCs) from the VDM self-test.

    Is DTC U3003:16 or U3003:17 present in the VDM? 

    Yes  If DTC U3003:16 is present, GO to Pinpoint Test A  If DTC U3003:17 is present, GO to Pinpoint Test B 
    No  GO to  G4

  5. G4 CHECK FOR DIAGNOSTIC TROUBLE CODES (DTCS) IN THE ABS (ANTI-LOCK BRAKE SYSTEM) MODULE

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

    Is DTC U3003:16 or U3003:17 present in the ABS module? 

    Yes  DIAGNOSE the ABS module Diagnostic Trouble Codes (DTCs). REFER to: Anti-Lock Brake System (ABS) and Stability Control .
    No  GO to  G5

  6. G5 CHECK FOR OTHER CAUSES OF COMMUNICATION NETWORK CONCERN

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

    • Check the vehicle service history for recent service actions related to the ABS module or VDM. If recent service history is found:

      • verify the correct replacement module was installed.

        • HVBOM may be used to verify correct part fitment.

      • verify the configuration of replacement module was correct.

        • re-configure the module using as-built data if prior configuration is suspect.

      • verify the module was not obtained from a like vehicle and installed into customer vehicle.

        • return the swapped module to source vehicle and obtain new replacement module.

    • Operate the system and determine if the observable symptom is still present.

    Is the observable symptom still present? 

    Yes  GO to  G6
    No  The system is operating correctly at this time. The concern may have been due to incorrect parts replacement procedures or incorrect module configuration.

  7. G6 CHECK FOR DTC (DIAGNOSTIC TROUBLE CODE) U0121:XX SET IN OTHER MODULES

    • Using a diagnostic scan tool, carry out the self-test for all modules.

    Is DTC U0121:xx set in 1 or more modules in addition to the VDM? 

    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 Technical Service Bulletins (TSBs) exist for this concern, INSTALL a new ABS module. REFER to: Anti-Lock Brake System (ABS) Module .
    No  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 Technical Service Bulletins (TSBs) exist for this concern, INSTALL a new VDM module. REFER to: Vehicle Dynamics Control Module (VDM) 
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