Endurant XD
TRTS0960 EN-US
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December 2024 - D

Fault Code 787: Rail C Calibration

J1939: SA 3 SPN 5953 FMI 7, 20, 21, 31

Overview

The Endurant XD Series transmissions are equipped with five Shift Rails: A, B, C, D, and E. The shift rails are mounted in shift rail cylinders in the Mechatronic Transmission Module (MTM). Solenoid valves direct vehicle Supply Air to and from the shift rail cylinders for shift rail actuation. Position sensors monitor shift rail positions and speed sensors monitor shaft speeds.

The sensor information is provided to the Transmission Control Module (TCM) for the purpose of making shift decisions, confirming gear engagement, and monitoring shift rail positions. The TCM routinely performs shift rail calibrations to ensure gear engagement and disengagement positions are within specifications. The TCM compares the shift rail commands to the shift rail positions and shaft speeds (ratio calculation) to ensure the transmission is operating properly.

The sensors and shift rails are located in the MTM and connected to the TCM at the 74-Way Transmission Harness Connector.

Detection

The TCM monitors the rail calibration. If a system failure is detected, the fault is set Active.

Conditions to Set Fault Code Active

FMI 7 – Mechanical System Not Responding: During a rail calibration, Rail C Position Sensor indicated no movement in aft direction.

FMI 20 – Data Drifted High: During a rail calibration, Rail C Position Sensor indicated insufficient movement in aft direction.

FMI 21 – Data Drifted Low: During a rail calibration, Rail C Position Sensor indicated insufficient movement in fore direction.

FMI 31 – Condition Exists: During a rail calibration, Rail C Position Sensor indicated no movement in fore direction.

Fallback

FMI 7, 20, 21, 31:

If Rail C position is known and Rail C is either fully engaged or fully disengaged:

  • Amber warning lamp on
  • Shift Rail C movement prohibited

If Rail C position is not known and Rail C is not fully engaged or fully disengaged:

  • Shift Rail C movement prohibited
  • Shift Rail D movement prohibited
  • Inertia Brake activation prohibited
  • Non-Neutral modes prohibited
  • PTO Mode prohibited
  • If vehicle is moving:
    • Red stop lamp on

Conditions to Set Fault Code Inactive

FMI 7, 20, 21, 31: Key on and fault condition no longer exists.

Possible Causes

FMI 7, 20, 21, 31:

  • MTM - Rail C
    • Rail C Solenoids
    • Rail C Cylinder
    • Rail C Detent
    • Rail C Yoke
    • Rail C Position Sensor
  • Internal transmission
    • Rail C Sliding Clutch
    • Main Shaft Assembly
    • Splitter Gear
    • Driven Gear 2nd

Additional Tools

  • Endurant XD Service Manual TRSM0960

Component Identification

_Graphics/LineArt/TRTS0960_FC215_ComponentID.png

1. Transmission Control Module (TCM) Cover

2. Transmission Control Module (TCM)

3. 74-Way Transmission Harness Connector (TCM-side)

4. 74-Way Transmission Harness Connector (MTM-side)

5. Transmission Control Module (TCM) Seal

6. MTM Air Inlet Port

Fault Code 787 Troubleshooting

A
Purpose:Check for active or inactive fault codes.

  1. Set the vehicle parking brake and chock wheels.

  2. Record transmission fault codes, FMIs, occurrences, and timestamps from Service Activity Report created during the Diagnostic Procedure.

B
Purpose:Verify condition of vehicle air system supply line and MTM air inlet port.

  1. Key off.

  2. Refer to OEM guidelines and vent vehicle air supply line to MTM.

  3. Refer to OEM guidelines and remove vehicle air supply line at MTM.

  4. Inspect vehicle air supply line and MTM air inlet port for contamination, moisture, corrosion and/or debris.

    Note: Verify MTM inlet screen is installed and free of contamination and/or debris.

    _Graphics/LineArt/TRTS0950_FC511_MTMAirInletPort.png

  • If contamination is found, refer to OEM guidelines for repair or replacement of vehicle air system. Replace Mechatronic Transmission Module (MTM) and Inertia Brake Assembly. Go to Step V

    Note: MTM removal and installation requires transmission be removed from vehicle. Reference Endurant XD Service Manual TRSM0960, Transmission Removal Service Procedure.

  • If no contamination is found, Go to Step C

C
Purpose:Verify mechanical condition of Splitter Gear and Driven Gear 2nd.

  1. Remove MTM.

    Note: MTM removal and installation requires transmission be removed from vehicle. Reference Endurant XD Service Manual TRSM0960, Transmission Removal Service Procedure.

  2. Inspect Splitter Gear for excessive fore and aft movement.

    _Graphics/LineArt/TRTS0960_FC295_D.png

  3. Inspect Driven Gear 2nd for excessive fore and aft movement.

  • If excessive gear movement is evident, inspect Main Shaft Assembly for cause and repair. Go to Step V

  • If no excessive gear movement is evident, Go to Step D

D
Purpose:Verify mechanical condition of Rail C Sliding Clutch and clutching teeth.

  1. Inspect Rail C Sliding Clutch yoke slot for wear.

    _Graphics/LineArt/TRTS0960_FC295_E.png

  2. Shift Rail C Sliding Clutch into neutral position (if necessary).

  3. Shift Rail C Sliding Clutch into Splitter Gear engagement position (fore).

  4. Inspect Driven Gear 2nd and Rail C Sliding Clutch clutching teeth for wear.

  5. Return Rail C Sliding Clutch to neutral position.

  6. Shift Rail C Sliding Clutch into Driven Gear 2nd engagement position (aft).

  7. Inspect Splitter Gear and Rail C Sliding Clutch clutching teeth for wear.

  8. Return Rail C Sliding Clutch to neutral.

V
Purpose:Verify repair.

  1. Key off.

  2. Reconnect all connectors and verify all components are properly installed.

  3. Key on with engine off.

  4. Connect ServiceRanger.

  5. Go To “Fault Codes”.

  6. Select “Clear All Faults”.

  7. Operate vehicle and attempt to reset the fault code or duplicate the previous complaint.

  8. Check for fault codes using ServiceRanger.