Fault Code 787: Rail C Calibration

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

Overview

The Endurant HD transmission is equipped with solenoids to direct pneumatic flow to actuate shift rails and sensors to monitor rail positions. The Transmission Control Module (TCM) compares the rail command and position to ensure proper rail operation. A Rail Calibration is performed to actuate each shift rail through all their positions. The shift rail positions are stored in memory and used to precisely actuate a shift rail during normal operation. The solenoids, positions 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 C Calibration. If a system failure is detected, the fault is set active.

Conditions to Set Fault Code Active

FMI 7 – Mechanical System Not Responding: Rail C Position Sensor indicated no movement in the Aft direction during a rail calibration.

FMI 20 – Data Drifted High: Rail C Position Sensor indicated insufficient movement in the Aft direction during a rail calibration.

FMI 21 – Data Drifted Low: Rail C Position Sensor indicated insufficient movement in the Fore direction during a rail calibration.

FMI 31 – Condition Exists: Rail C Position Sensor indicated no movement in the Fore direction during a rail calibration.

Fallback

FMI 7, 20, 21, 31:

  • If Rail C position is known and fully engaged
    • Amber warning lamp on
    • Shift Rail C movement prohibited
  • If Rail C position is not known or not fully engaged:
    • Amber warning lamp on
    • Shift Rail C movement prohibited
    • Shift Rail D movement prohibited
    • Non neutral modes prohibited
    • Urge to Move and Creep Mode prohibited
    • PTO Mode Prohibited
    • If vehicle is moving - Red stop lamp on

Conditions to Set Fault Code Inactive

FMI 7, 20, 21, 31: Successful Rail Calibration

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
    • Primary Drive Gear
    • Secondary Driven Gear

Additional Tools

  • Endurant HD Service Manual TRSM0950

Component Identification

_Graphics/LineArt/TRTS0950_FC511_ComponentID.png

1. Transmission Control Module (TCM) Cover

2. Transmission Control Module (TCM)

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

4. 74-Way Transmission Harness Connector (TCM-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 the transmission fault codes, FMIs, occurrences, and timestamps from the Service Activity Report created during the Diagnostic Procedure.

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

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

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

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

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

    _Graphics/LineArt/TRTS0950_FC511_MTMAirInletPort.png
C
Purpose:Verify mechanical condition of the Primary Drive and Secondary Driven Gears.
  1. Key off.

  2. Remove the MTM.

    Note: MTM removal and installation requires the transmission to be removed from the vehicle. Reference Endurant HD Service Manual TRSM0950, Transmission Removal Service Procedure.

  3. Inspect the Primary Drive Gear for excessive fore and aft movement.

    _Graphics/LineArt/TRTS0950_FC760_Gears.png
  4. Inspect the Secondary Driven Gear for excessive fore and aft movement.

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

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

D
Purpose:Verify mechanical condition of the Rail C Sliding Clutch and clutching teeth.
  1. Inspect the Rail C Sliding Clutch yoke slot for wear.

    _Graphics/LineArt/TRTS0950_FC295_CSlidingClutch.png
  2. Shift the Rail C Sliding Clutch to the neutral position (if necessary).

  3. Shift the Rail C Sliding Clutch into the Primary Drive Gear engagement position (fore).

  4. Inspect the Rail C Sliding Clutch clutching teeth for wear.

  5. Return the Rail C Sliding Clutch to neutral.

  6. Shift the Rail C Sliding Clutch into the Secondary Driven Gear engagement position (aft).

  7. Inspect the Rail C Sliding Clutch clutching teeth for wear.

  8. Return the Rail C Sliding Clutch to neutral.

V
Purpose:Verify repair.
  1. Key off.

  2. Reconnect all connectors and verify that 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.