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Normal Operation and Fault Conditions

With the ignition ON, the ABS module sends messages to the SASM over the HS-CAN 2. If the SASM does not receive these messages within a certain time frame (usually less than 1 second), the SASM sets DTCs. 

PPT AX SASM DTC FAULT TRIGGER CONDITIONS

DTC Description Fault Trigger Conditions
U0121:00 Lost Communication With Anti-Lock Brake System (ABS) Control Module: No Sub Type Information Sets in continuous memory and on-demand when the SASM detects any of the ABS module messages are missing. This can be due to a ABS module failure, a circuit failure on the HS-CAN or an excessive load on the network.

Possible Causes 

  1. AX1: CHECK THE COMMUNICATION NETWORK 
    • Ignition ON, engine OFF.
    • Press the Read Vehicle Information button to view the results of the modules communicating on the network.
    • Retrieve the continuous memory DTCs.
    • Does the ABS module pass the Network Test? 
      Yes No
      Go to  AX2. DIAGNOSE the scan tool does not communicate with the ABS module. REFER to MODULE COMMUNICATIONS NETWORK .
  2. AX2: REPEAT THE SASM SELF-TEST AND CHECK IF THE DTC SETS AGAIN 
    • Carry out the SASM self-test.
    • Clear the SASM DTCs.
    • Ignition OFF.
    • Ignition ON, engine OFF.
    • Carry out the SASM self-test.
    • Is DTC U0121:xx still present? 
      Yes No
      Go to  AX3. The system is operating correctly at this time. The DTC may have been set due to high network traffic or an intermittent fault condition.
  3. AX3: REVIEW THE SASM SELF-TEST FOR VOLTAGE-REALTED DTCS 
    • Review the results from the SASM self-test.
    • Is DTC U3003:1C or U3003:17 present? 
      Yes No
      For DTC U3003:1C, Go to PINPOINT TEST BD .
      For DTC U3003:17, Go to PINPOINT TEST BE .
      For all others, No fault found.      		 Go to  AX4.
  4. AX4: CHECK FOR ABS MODULE DTCS 
    • Carry out the ABS self-test.
    • Are any DTCs present? 
      Yes No
      DIAGNOSE the ABS module DTC. REFER to the ABS Module DTC Chart . Go to  AX5.
  5. AX5: 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 SASM. 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.
      Yes No
      Go to  AX6. The system is operating correctly at this time. The concern may have been due to incorrect parts replacement procedures or incorrect module configuration.
  6. AX6: VERIFY ALL WIRING CONNECTIONS 
    • Ignition OFF.
    • Disconnect all SASM connectors.
    • Disconnect the ABS module connector.
    • Disconnect all in-line electrical connectors between the SASM and the ABS module.
    • Using a good light source, inspect all disconnected electrical connectors for the following:
      • corrosion - install new connector or terminal and clean the module pins
      • damaged or bent pins - install new terminals or pins
      • pushed-out pins - install new pins as necessary
      • spread terminals - install new terminals as necessary
    • Are the connectors free of corrosion, damaged pins, bent pins, pushed-out pins and spread terminals? 
      Yes No
      Go to  AX7. REPAIR the connector or terminals. Refer to OEM CONNECTOR REPAIR PROCEDURES , for schematic and connector information.
  7. AX7: CHECK FOR DTC U0121:XX SET IN OTHER MODULES 
    • Connect all SASM electrical connectors. Make sure they seat and latch correctly.
    • Connect the ABS module connector. Make sure it seats and latches correctly.
    • Connect all in-line electrical connectors between the SASM and the ABS module. Make sure they seat and latch correctly.
    • Ignition ON, engine OFF.
    • Press the Read Vehicle Information button to view the results of the continuous DTCs set in other modules.
    • Retrieve the continuous memory DTCs.
    • Review the CMDTCs from all modules.
    • Is DTC U0121:xx set in other modules in addition to the SASM? 
      Yes No
      INSTALL a new ABS module.
      CHECK OASIS for any applicable Technical Service Bulletins TSBs.
      If a TSB exists for this concern, DISCONTINUE this test and FOLLOW the TSB instructions.
      If no TSBs address this concern, INSTALL a new ABS module. REFER to the appropriate Removal and Installation procedure in ANTI-LOCK BRAKE SYSTEM (ABS) AND STABILITY CONTROL .      		 CHECK OASIS for any applicable TSBs.
      If a TSB exists for this concern, DISCONTINUE this test and FOLLOW the TSB instructions.
      If no TSBs address this concern, INSTALL a new SASM-clockspring. REFER to the appropriate REMOVAL AND INSTALLATION .
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