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Pinpoint Test G : U0121:00

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  1. Refer to OEM WIRING DIAGRAMS COMPONENT TESTING for schematic and connector information.

    Normal Operation and Fault Conditions 

    The TCM sets the DTC U0121 when key messages such as wheel speed, brake pressure or torque are not received for longer than 5 seconds. Other modules that require data from the ABS module all set communication DTCs and may also exhibit system concerns.

    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 Sets in continuous memory in the TCM if ABS data messages received from the ABS Module over the HS-CAN are missing for longer than 2 seconds.

    Possible Sources 

    • Communication concern
    • Battery voltage concern
    • GWM concern
    • ABS
    • TCM

  2. G1 VERIFY THE CUSTOMER CONCERN

    • Ignition ON.

    • Verify there is an observable symptom present.

    Is an observable symptom present? 

    Yes  GO to  G2
    No  CLEAR the DTC. The system is operating normally at this time. The DTC may have been set due to high network traffic or an intermittent fault condition.

  3. G2 CHECK THE COMMUNICATION NETWORK

    • Ignition ON.

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

    Does the ABS pass the network test? 

    Yes  GO to  G3
    No  REFER to: Communications Network .

  4. G3 CHECK THE TCM (TRANSMISSION CONTROL MODULE) CONTINUOUS MEMORY DIAGNOSTIC TROUBLE CODES (CM DTCs)

    • Ignition ON.

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

    • Clear the DTCs.

    • Wait 10 seconds.

    • Repeat the TCM self-test.

    Are any non-network Diagnostic Trouble Codes (DTCs) present? 

    Yes  DIAGNOSE all non-network DTCs. REFER to DTC Chart: TCM 
    No  GO to  G4

  5. G4 PERFORM THE ABS (ANTI-LOCK BRAKE SYSTEM) SELF-TEST

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

    Are any non-network Diagnostic Trouble Codes (DTCs) present? 

    Yes  DIAGNOSE all non-network DTCs.
    No  GO to  G5

  6. G5 CHECK THE GWM (GATEWAY MODULE A) DIAGNOSTIC TROUBLE CODES (DTCs)

    • Using a diagnostic scan tool, check the GWM Continuous Memory Diagnostic Trouble Codes (CM DTCs).

    Are any Diagnostic Trouble Codes (DTCs) recorded? 

    Yes  REFER to: Communications Network .
    No  GO to  G6

  7. G6 RECHECK THE TCM (TRANSMISSION CONTROL MODULE) DIAGNOSTIC TROUBLE CODES (DTCs)

    • Using a diagnostic scan tool, clear the TCM DTCs.

    • Ignition OFF.

    • Ignition ON.

    • Wait 10 seconds.

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

    • Check the TCM DTCs.

    Is DTC U0121:00 still present? 

    Yes  GO to  G7
    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.

  8. G7 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 or TCM. If recent service history is found:

      • verify correct replacement module was installed

        • HVBOM may be used to verify correct part fitment

      • verify the configuration of replacement module was correct

        • re-configure 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  G8
    No  The system is operating correctly at this time. The concern may have been due to incorrect parts replacement procedures or incorrect module configuration.

  9. G8 CHECK FOR CORRECT ABS (ANTI-LOCK BRAKE SYSTEM) OPERATION

    • Ignition OFF.

    • Disconnect and inspect the ABS and related in-line 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 and all related in-line 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 Technical Service Bulletins (TSBs). If a TSB exists for this concern, DISCONTINUE this test and FOLLOW TSB instructions. If no Technical Service Bulletins (TSBs) 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.
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