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Home >> Lincoln >> 2018 >> Navigator Select, 4WD >> Repair and Diagnosis >> Restraints >> Restraints Control Systems >> RCM Guided Routine Testing -- (2 Of 4) >> Pinpoint Tests >> Pinpoint Test AU: Lost Communication with ABS >> Possible Causes

Possible Causes

WARNING: Incorrect repair techniques or actions can cause an accidental SRS deployment. Never compromise or depart from these instructions. Failure to precisely follow all instructions could result in serious personal injury from an accidental deployment.
NOTE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may cause damage to the connector.
NOTE: Most faults are due to connector and/or wiring concerns. Carry out a thorough inspection and verification before proceeding with the pinpoint test.
NOTE: Only disconnect or reconnect SRS components when instructed to do so within a pinpoint test step. Failure to follow this instruction may result in incorrect diagnosis of the SRS.
NOTE: Always make sure the correct SRS component is being installed. Parts released for other vehicles may not be compatible even if they appear physically similar. Check the part number listed in the parts catalog to make sure the correct component is being installed. If an incorrect SRS component is installed, DTCs may set.
NOTE: The SRS must be fully operational and free of faults before releasing the vehicle to the customer.
Fig 1: Restraint Control Module-B (RCM-B) Connector End View (C310B)
G12765504Courtesy of FORD MOTOR CO.
Harness Side

Circuit Pin
  1. AU1: RETRIEVE RCM DTCS 
    • Ignition ON, engine OFF.
    • Carry out the RCM self-test.
    • Is DTC U0028:08 or U0028:88 retrieved on-demand during self-test? 
      Yes No
      This fault cannot be cleared until it is corrected and the DTC is no longer retrieved on-demand during self-test.
      For DTC U0028:08, Go to  AU2.
      For DTC U0028:88, Go to  AU5.      		 This is an intermittent fault when present as a CMDTC only.
      Go to  AU14.
  2. AU2: CHECK FOR CORRECT RCM PART NUMBER 
    • Using the Log Viewer function of the diagnostic scan tool, retrieve and record the RCM part number.
    • Check the part number recorded against the number listed in the parts catalog and verify the correct RCM is present
    • Is the correct RCM installed? 
      Yes No
      Go to  AU3. INSTALL the correct RCM. REFER to Restraints Control Module (RCM) in Supplemental Restraint System article.
      Go to  AU15.
  3. AU3: CHECK FOR CORRECT ABS MODULE PART NUMBER 
    • Using the Log Viewer function of the diagnostic scan tool, retrieve and record the ABS module part number.
    • Check the part number recorded against the number listed in the parts catalog and verify the correct ABS module is present in the vehicle.
    • Is the correct ABS module installed? 
      Yes No
      Go to  AU4. INSTALL the correct ABS module. REFER to Anti-Lock Brake System (ABS) and Stability Control article
      Go to  AU15.
  4. AU4: CHECK THE HS-CAN COMMUNICATIONS (ABS MODULE COMMUNICATIONS) 
    • Ignition ON, engine OFF.
      NOTE: The Network Test does not test the dedicated CAN communications between the ABS module and RCM.
    • Enter the following diagnostic mode on the scan tool: Network Test.
    • Does the Network Test pass (ABS module communicates with the scan tool)? 
      Yes No
      Go to  AU5. REFER to Module Communications Network article to diagnose the HS-CAN/ABS module communication concern.
      Go to  AU15.
  5. AU5: CHECK THE DEDICATED CAN CIRCUITS FOR AN OPEN 
    • Ignition OFF.
    • Depower the SRS. Refer to Supplemental Restraint System (SRS) Depowering in Supplemental Restraint System article.
    • RCM_A connector disconnected. (C310A)
    • RCM_B connector disconnected. (C310B)
    • ABS Module connector disconnected.
    • Measure the resistance between:
      (+) ABS Module Connector, Harness Side (-) RCM_B (C310B) Connector, Harness Side
      HS_CAN_YAW+ HS_CAN_YAW+
      HS_CAN_YAW- HS_CAN_YAW-
    • Are the resistances less than 5 ohms? 
      Yes No
      Go to  AU9. REPAIR the circuit in question.
      Go to  AU15.
  6. AU6: CHECK THE DEDICATED CAN CIRCUITS FOR A SHORT TO VOLTAGE 
    • Ignition OFF.
    • Depower the SRS. Refer to Supplemental Restraint System (SRS) Depowering in Supplemental Restraint System article.
    • Repower the SRS. REFER to the Supplemental Restraint System (SRS) Repowering in the General Procedures portion of Supplemental Restraint System article
    • Ignition ON, engine OFF.
    • Measure the voltage between:
      (+) ABS Module Connector, Harness Side (-)
      HS_CAN_YAW+ Ground
      HS_CAN_YAW- Ground
    • Is any voltage present? 
      Yes No
      REPAIR the circuit(s) in question.
      Go to  AU15.      		 Go to  AU7.
  7. AU7: CHECK THE DEDICATED CAN CIRCUITS FOR A SHORT TO GROUND 
    • Ignition OFF.
    • Depower the SRS. Refer to Supplemental Restraint System (SRS) Depowering in Supplemental Restraint System article.
    • Measure the resistance between:
      (+) ABS Module Connector, Harness Side (-)
      HS_CAN_YAW+ Ground
      HS_CAN_YAW- Ground
    • Are the resistance's greater than 10, 000 ohms? 
      Yes No
      Go to  AU8. REPAIR the circuit.
      Go to  AU15.
  8. AU8: CHECK FOR SHORT BETWEEN THE DEDICATED CAN CIRCUITS 
    • Measure the resistance between:
      (+) ABS Module Connector, Harness Side (-) ABS Module Connector, Harness Side
      HS_CAN_YAW+ HS_CAN_YAW-
    • Is the resistance greater than 10, 000 ohms? 
      Yes No
      Go to  AU9. REPAIR the circuit.
      Go to  AU15.
  9. AU9: CHECK THE RCM TERMINATING RESISTOR 
    • Depower the SRS. Refer to Supplemental Restraint System (SRS) Depowering in Supplemental Restraint System article.
    • RCM_B connector connected. (C310B)
    • Measure the resistance between:
      (+) ABS Module Connector, Harness Side (-) ABS Module Connector, Harness Side
      HS_CAN_YAW+ HS_CAN_YAW-
    • Is the resistance between 108 and 132 ohms? 
      Yes No
      Go to  AU10. Go to  AU11.
  10. AU10: CHECK THE ABS MODULE TERMINATING RESISTOR 
    • RCM_B connector disconnected. (C310B)
    • ABS Module connector connected.
    • Measure the resistance between:
      (+) RCM_B (C310B) Connector, Harness Side (-) RCM_B (C310B) Connector, Harness Side
      HS_CAN_YAW+ HS_CAN_YAW-
    • Is the resistance between 108 and 132 ohms? 
      Yes No
      For DTC U0028:08, Go to  AU11.
      For DTC U0028:88, Go to  AU13.      		 Go to  AU13.
  11. AU11: CONFIRM THE RCM FAULT 
    NOTE: Make sure all SRS components and the RCM electrical connectors are connected before carrying out the self-test. If not, DTCs are recorded.
    • Ignition OFF.
    • If previously directed to repower the SRS, depower the SRS. Refer to Supplemental Restraint System (SRS) Depowering in Supplemental Restraint System article.
    • Prior to reconnecting any previously disconnected SRS component:
      • inspect connector(s) (including any inline connectors) for pushed-out, loose or spread terminals and loose or frayed wire connections at terminals.
      • inspect wire harness for any damaged, pinched, cut or pierced wires.
      • inspect the RCM electrical connectors and the Connector Position Assurance (CPA) levers/locks for correct operation.
      • inspect ABS module C135 for dirt, corrosion, water intrusion, pushed-out, loose or spread terminals and loose or frayed wire connections at terminals.
      • repair any concerns found. Refer to OEM GROUND DISTRIBUTION article, for schematic and connector information.
    • Connect: All Previously Disconnected Component(s)/Connector(s).
    • Connect the RCM electrical connectors. Make sure they latch and seat correctly.
    • Repower the SRS. Do not prove out the SRS at this time. Refer to Supplemental Restraint System (SRS) Repowering in Supplemental Restraint System article.
    • Ignition ON, engine OFF.
    • Carry out the RCM self-test.
    • Is the original DTC retrieved on-demand during self-test? 
      Yes No
      INSTALL a new RCM. REFER to Restraints Control Module (RCM) in Supplemental Restraint System article.
      Go to  AU12.      		 In the process of diagnosing the fault, the fault condition has become intermittent. Do not install any new SRS components at this time.
      Install SRS components only when directed to do so in the pinpoint test.
      Go to  AU14.
  12. AU12: CONFIRM THE REPAIR 
    • Ignition OFF.
    • CHECK OASIS for any applicable TSBs.
      • If a TSB exists for this concern, DISCONTINUE this test and FOLLOW TSB instructions.
      • If no TSBs address this concern, INSTALL a new RCM. Refer to the appropriate Removal and Installation procedure in Supplemental Restraint System article.
      Yes No
      INSTALL a new RCM.
      Reconnect all previously disconnected SRS components and repower the SRS.
      REFER to the Supplemental Restraint System (SRS) Repowering in the General Procedures portion of Supplemental Restraint System article
      Carry out the OCSM and RCM self-test and record DTCs if present. Do not clear any DTCs until all DTCs have been resolved. DIAGNOSE and REPAIR the RCM and/or OCSM DTCs.
      Carry out the OCSM and RCM self-test and record DTCs if present. Do not clear any DTCs until all DTCs have been resolved.
      If any SRS DTCs are retrieved, DO NOT clear any DTCs until all DTCs have been resolved.
      DIAGNOSE and REPAIR the RCM and/or OCSM DTCs.
      If no DTCs are retrieved on-demand, the repair is complete. RETURN the vehicle to the customer.      		  
  13. AU13: CONFIRM THE ABS MODULE FAULT 
    NOTE: Make sure all restraint system components and the RCM electrical connectors are connected before carrying out self-test. If not, DTCs will be recorded.
    • If previously directed to repower the SRS, depower the SRS. Refer to Supplemental Restraint System (SRS) Depowering in Supplemental Restraint System article.
    • Prior to reconnecting any previously disconnected SRS component:
      • inspect connector(s) (including any inline connectors) for pushed-out, loose or spread terminals and loose or frayed wire connections at terminals.
      • inspect wire harness for any damaged, pinched, cut or pierced wires.
      • inspect the RCM electrical connectors and the Connector Position Assurance (CPA) levers/locks for correct operation.
      • inspect ABS module for dirt, corrosion, water intrusion, pushed-out, loose or spread terminals and loose or frayed wire connections at terminals.
      • repair any concerns found. Refer to OEM GROUND DISTRIBUTION article, for schematic and connector information.
    • Connect: All Previously Disconnected Component(s)/Connector(s).
    • Repower the SRS. Do not prove out the SRS at this time. Refer to Supplemental Restraint System (SRS) Repowering in Supplemental Restraint System article.
    • Ignition ON, engine OFF.
    • Carry out the RCM self-test.
    • Is the original DTC retrieved on-demand during self-test? 
      Yes No
      INSTALL a new ABS module. REFER to the ABS Module Removal and Installation in Anti-Lock Brake System (ABS) and Stability Control article
      Go to  AU15.      		 In the process of diagnosing the fault, the fault condition has become intermittent.
      Do not install any new SRS components at this time. SRS components should only be installed when directed to do so in the pinpoint test.
      Go to  AU14.
  14. AU14: CHECK FOR AN INTERMITTENT FAULT 
    • Ignition OFF.
    • Depower the SRS. Refer to Supplemental Restraint System (SRS) Depowering and Repowering in Supplemental Restraint System article.
    • RCM_A connector disconnected. (C310A)
    • RCM_B connector disconnected. (C310B)
    • ABS Module connector disconnected.
      • inspect connector(s) (including any in-line connectors) for corrosion, loose or spread terminals and loose or frayed wire connections at terminals.
      • inspect wire harness for any damage, pinched, cut or pierced wires.
      • repair any concerns found. Refer to OEM GROUND DISTRIBUTION article, Connector Repair Procedures for schematic and connector information.
      • inspect the RCM electrical connectors and the Connector Position Assurance (CPA) levers/locks for correct operation.
      • inspect ABS electrical connector for dirt, corrosion, water intrusion, pushed-out, loose or spread terminals and loose or frayed wire connections at terminals.
    • Connect: All Previously Disconnected Component(s)/Connector(s).
    • Repower the SRS. Do not prove out the SRS at this time. Refer to Supplemental Restraint System (SRS) Repowering in Supplemental Restraint System article.
    • Ignition ON, engine OFF.
    • Carry out the RCM self-test.
    • Is DTC U0028:08 or U0028:88 retrieved on-demand during self-test? 
      Yes No
      This fault cannot be cleared until it is corrected and the DTC is no longer retrieved on-demand during self-test.
      CHECK for causes of the intermittent fault in the areas previously worked in, particularly the pins and terminals of any electrical connector that were disconnected. REPAIR any intermittent wiring, terminal or connector concerns found. Refer to OEM GROUND DISTRIBUTION article, Connector Repair Procedures for schematic and connector information.
      Go to  AU15.      		 The fault is not present and cannot be recreated at this time. Do not install any new SRS components at this time. SRS components should only be installed when directed to do so in the pinpoint test.
      Go to  AU15.
  15. AU15: CHECK FOR ADDITIONAL RCM AND ABS MODULE DTCS 
    • Ignition OFF.
      WARNING: Turn the ignition OFF and wait one minute to deplete the backup power supply. Failure to follow this instruction may result in serious personal injury or death in the event of an accidental deployment.
    • Reconnect all SRS components (if previously disconnected).
    • If previously directed to depower the SRS, repower the SRS. Refer to Supplemental Restraint System (SRS) Depowering in Supplemental Restraint System article.
    • Ignition ON, engine OFF.
    • Carry out the RCM self-test.
    • Carry out the ABS self-test.
    • Are any DTCs retrieved from the RCM or ABS module during self-test? 
      Yes No
      Do not clear any DTCs until all DTCs have been resolved. GO to the appropriate DTC Chart and/or Anti-Lock Brake System (ABS) and Stability Control article for pinpoint test direction. CLEAR all CMDTCs. PROVE OUT the SRS. Repair is complete. RETURN the vehicle to the customer.
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