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Pinpoint Test A : U0121

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  1. Normal Operation and Fault Conditions 

    DTC Fault Trigger Conditions 

    DTC Description Fault Trigger Condition
    PCM U0121:00 Lost Communication With Anti-Lock Brake System (ABS) Control Module "A": No Sub Type Information The PCM sets this DTC if data messages from the ABS module through the GWM are missing.

    Possible Sources 

    • Communications network concern
    • ABS module
    • GWM
    • PCM

  2. A1 VERIFY THE CUSTOMER CONCERN

    • Ignition ON.

    • Verify there is an observable symptom present.

    Is an observable symptom present? 

    Yes  GO to  A2
    No  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. A2 CHECK THE COMMUNICATION NETWORK

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

    Did the ABS module pass the network test? 

    Yes  GO to  A3
    No 

  4. A3 PERFORM ABS (ANTI-LOCK BRAKE SYSTEM) CONTROL MODULE SELF-TEST

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

    Are any Diagnostic Trouble Codes (DTCs) recorded? 

    Yes  Without stability control, REFER to: Anti-Lock Brake System (ABS) . With stability control, REFER to: Anti-Lock Brake System (ABS) and Stability Control .
    No  GO to  A4

  5. A4 CHECK THE BCM (BODY CONTROL MODULE) DIAGNOSTIC TROUBLE CODES (DTCS)

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

    Are any Diagnostic Trouble Codes (DTCs) recorded? 

    Yes 
    No  GO to  A5

  6. A5 PERFORM THE PCM (POWERTRAIN CONTROL MODULE) SELF-TEST

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

    Is DTC P0562 or DTC P0563 recorded? 

    Yes  REFER to DTC Chart: Powertrain Control Module (PCM) .
    No  GO to  A6

  7. A6 RECHECK THE PCM (POWERTRAIN CONTROL MODULE) DIAGNOSTIC TROUBLE CODES (DTCS)

    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.

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

    • Wait 10 seconds.

    • Repeat the PCM self-test.

    Is DTC U0121 still present? 

    Yes  GO to  A7
    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. A7 CHECK FOR DTC (DIAGNOSTIC TROUBLE CODE) U0121 SET IN OTHER MODULES

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

    • Ignition OFF.

    • Ignition ON.

    • Wait 10 seconds.

    • Using a diagnostic scan tool, retrieve all Continuous Memory Diagnostic Trouble Codes (CMDTCs) from all modules.

    Is DTC U0121:00 set in any other module? 

    Yes  GO to  A8
    No  GO to  A9

  9. A8 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 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 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. 206-09 RI
    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.

  10. A9 CHECK FOR CORRECT PCM (POWERTRAIN CONTROL MODULE) OPERATION

    • Ignition OFF.

    • Disconnect and inspect the PCM 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 PCM 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, Refer to PCM GUIDED ROUTINE TESTING
    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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