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Pinpoint Test E: DTC U0121

  1. Refer to Wiring Diagrams MODULE COMMUNICATIONS NETWORK for schematic and connector information.

    Normal Operation and Fault Conditions 

    The DTC sets if there is a loss or gap in module communications for more than 5 seconds. Modules that don't communicate with the scan tool are obvious concerns.

    DTC Fault Trigger Conditions 

    DTC Description Fault Trigger Condition
    GSM U0121:00 Lost Communication With Anti-Lock Brake System (ABS) Control Module "A": No Sub Type Information Sets in continuous memory in the GSM if data messages received from the ABS are missing for 5 seconds or longer.

    Possible Sources 

    • Communication concern
    • ABS
    • GSM

  2. E1 VERIFY THE SCAN TOOL COMMUNICATES WITH THE ABS (ANTI-LOCK BRAKE SYSTEM)

    • Ignition ON.

    • Connect the diagnostic scan tool.

    • Check that a vehicle session can be established using the scan tool.

    Can a vehicle session be established? 

    Yes  GO to  E2
    No  REFER to: Controller Area Network (CAN) Module Communications Network
     

  3. E2 CHECK THE GSM (GEAR SHIFT MODULE) CONTINUOUS MEMORY DIAGNOSTIC TROUBLE CODES (CMDTCS)

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

    • Clear the DTCs.

    • Wait 10 seconds.

    • Repeat the GSM self-test.

    Are any non-network DTCs present? 

    Yes  DIAGNOSE all non-network DTCs. REFER to GSM: DTC Chart .
    No  GO to  E3

  4. E3 PERFORM THE ABS (ANTI-LOCK BRAKE SYSTEM) SELF-TEST

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

    Are any non-network DTCs present? 

    Yes  DIAGNOSE all non-network DTCs. REFER to: Anti-Lock Brake System (ABS) and Stability Control
     
    No  GO to  E4

  5. E4 CHECK THE GWM (GATEWAY MODULE A) DIAGNOSTIC TROUBLE CODES (DTCS)

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

    Are any DTCs set? 

    Yes  REFER to: Controller Area Network (CAN) Module Communications Network
     
    No  GO to  E5

  6. E5 RECHECK THE GSM (GEAR SHIFT MODULE) DIAGNOSTIC TROUBLE CODES (DTCS)

    • Using a diagnostic scan tool, clear the GSMDTCs.

    • Ignition OFF.

    • Ignition ON.

    • Wait 10 seconds.

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

    • Check the GSMDTCs.

    Is DTC U0121 still present? 

    Yes  GO to  E6
    No  The system is operating correctly at this time. The DTC may have set due to high network traffic or an intermittent fault condition.

  7. E6 CHECK FOR OTHER CAUSES OF NETWORK COMMUNICATION CONCERNS

    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 AWD. If recent service history is found:

      • verify correct replacement module was installed

        • HVBOM may be used to verify correct part application

      • 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  E7
    No  The system is operating correctly at this time. The concern may have been due to incorrect parts replacement procedures or incorrect module configuration.

  8. E7 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 ABS 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 service articles: TSB, GSB (general service bulletin), SSM (special service message) or FSA (Field Service Action). If a service article exists for this concern, DISCONTINUE this test and FOLLOW the service article instructions. If no service articles address this concern, Refer to ABS GUIDED ROUTINE
    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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