Fault Code 788: Rail D Calibration (TRTS0950) (2024)

Fault Code 788: Rail D Calibration

J1939: SA 3 SPN 5954 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 D position during a 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: Rail D Position Sensor indicated no movement in the Aft direction during a rail calibration.

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

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

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

Fallback

FMI 7, 20, 21, 31:

  • If Rail D position is known and fully engaged
    • Amber warning lamp on
    • Shift Rail D movement prohibited
  • If Rail D 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
    • PTO Mode prohibited
    • If vehicle is moving - Red stop lamp on

Conditions to Set Fault Code Inactive

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

Possible Causes

FMI 7, 20, 21, 31:

  • MTM - Rail D
    • Rail D Solenoids
    • Rail D Cylinder
    • Rail D Detent
    • Rail D Yoke
    • Rail D Position Sensor
  • Internal Transmission
    • Rail D Sliding Clutch
    • Main Shaft Assembly
    • Primary Driven Gear
    • Reverse Gear

Additional Tools

  • Endurant HD Service Manual TRSM0950

Component Identification

Fault Code 788: Rail D Calibration (TRTS0950) (1)

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 788 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.

  • If Fault Code 788 is Active or Inactive, Go to Step B

B

Purpose:Verify mechanical condition of the Primary Driven Gear and Reverse Gear.

  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.

    Fault Code 788: Rail D Calibration (TRTS0950) (2)

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

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

  • If no contamination is found, Go to Step C

C

Purpose:Verify mechanical condition of the Primary Driven Gear and Reverse Gear.

  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 Driven Gear for excessive fore and aft movement.

    Fault Code 788: Rail D Calibration (TRTS0950) (3)

  4. Inspect the Reverse 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 D Sliding Clutch and clutching teeth.

  1. Inspect the Rail D Sliding Clutch yoke slot for wear.

    Fault Code 788: Rail D Calibration (TRTS0950) (4)

  2. Shift the Rail D Sliding Clutch to the neutral position (if necessary).

  3. Shift the Rail D Sliding Clutch into the Primary Driven Gear engagement position (fore).

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

  5. Return the Rail D Sliding Clutch to neutral.

  6. Shift the Rail D Sliding Clutch into the Reverse Gear engagement position (aft).

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

  8. Return the Rail D Sliding Clutch to neutral.

  • If the Rail D Sliding Clutch shifts into all three positions and no clutching teeth wear is present, replace the Mechatronic Transmission Module (MTM). Go to Step V

  • If the Rail D Sliding Clutch does not shift into all three positions or clutching teeth wear is present, inspect the Main Shaft; replace the Rail D Sliding Clutch, Primary Driven Gear, Reverse Gear and Mechatronic Transmission Module (MTM). Go to Step V

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.

  • If no fault codes set and the vehicle operates properly, test complete.

  • If Fault Code 788 sets Active during operation, Go to Step A

  • If a fault code other than 788 sets Active, troubleshoot per the Fault Code Isolation Procedure Index.

Fault Code 788: Rail D Calibration (TRTS0950) (2024)

FAQs

What is the fault code spn 788 fmi 7? ›

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

How do you retrieve the fault code on the Eaton Ultrashift? ›

To Retrieve Inactive Codes: Turn key on. Turn the key off and on 4 times within five seconds ending with the key in the on position. After 5 seconds, the Service light begins flashing two-digit fault codes. If no faults are active, the service light will flash code 25 (no codes).

What is the fault code 88 on Eaton transmission? ›

Fallback When Fault Code 88 is set the following conditions occur: Amber “Check Hybrid” light illuminates. Fault is stored in Hybrid Control Module (HCM) memory. Electric Motor/Generator Assist and Regeneration are disabled; however, the high-voltage relays remain powered.

What is a clutch actuator? ›

The clutch actuator is part of the overall clutch system and can operate either mechanically or hydraulically. With a clutch actuation system, the driver controls the interruption of power transmission. by pressing the pedal.

What does FMI 7 mean? ›

A component failure would look like an FMI 12 for bad device/component or an FMI 7 for a component not responding or being out of adjustment.

How do you calibrate an Eaton UltraShift clutch? ›

Select the “Clear Clutch Data” button to clear data from transmission controller. If successful proceed to next step, if unsuccessful exit function and re-enter. Contact Roadranger Call Center 1-800-826-4357 for help. Select the “Calibrate Clutch” button to calibrate new cultch and then Select “Finish” when complete.

Where is the ECA speed sensor located? ›

The ECA Speed Sensor is installed in the clutch housing. The ECA broadcasts the ECA Speed Sensor signal to the TECU through the High Integrity Link (HIL) contained within the transmission harness.

Should I reset my transmission control module? ›

When to Reset the Transmission Control Module. Resetting the TCM won't fix severe transmission issues, but it does clear errors. Some scenarios where rebooting the module could be necessary include delayed shifting, stuck gears, and poor fuel economy.

How do I reset my shift module? ›

Turn off your vehicle's ignition and wait patiently for 5 to 10 seconds. Start the engine and allow it to idle for several seconds. Switch off the ignition and wait patiently for another 30 to 40 seconds. Repeat these steps 2 to 3 times in order to reset your vehicle's transmission control module.

What does GI mean on Eaton transmission? ›

“AN” will appear in the gear display if the transmission goes into Auto Neutral. In heavy-duty UltraShift™ PLUS Automated models, “GI” may briefly appear in the gear display after the engine is started. This indicates that the clutch release bearing will need to be greased soon.

How do I clear my Eaton code? ›

Clearing Fault Codes

Turn the key OFF and ON six times within five seconds, ending with the key in the ON position. Note: If the codes have been successfully cleared, the service lamp will come on and stay on for five seconds. 2. T urn the key OFF and allow system to power down.

What is the code for a failing transmission? ›

The P0700 code indicates a problem with the transmission.

What is code 19 on Eaton automatic transmission? ›

Fault Code 19 indicates a loss of communication between the TECU and ECA.

What does SPN and FMI mean? ›

SPN stands for Suspected Parameter Number which tells you the circuit where the fault occurred. For example, if you had a SPN 1791 code, it would point to a fault detected in the EGR Valve Control Circuit. FMI stands for Failure Mode Indicator which tells you the reason the fault code was set.

What does SPN mean on engine? ›

SPN stands for Suspect Parameter Number. It's a diagnostic trouble code that provides detailed information about specific faults detected by the vehicle's ECU, making it easier to identify and address issues within the vehicle's electronic systems.

What is the failure mode identifier FMI? ›

Failure Mode Indication (FMI), as part of the J1939 standard used in heavy-duty vehicles, functions by closely monitoring system components. When a fault occurs, FMI generates a precise code that identifies the specific nature of the issue, much like an advanced version of a 'check engine' light.

What is fault code 64 FMI 7? ›

FMI 7 – Mechanical System Not Responding: ECA detects excessive motor current or ECA detects incorrect clutch position during a clutch position change for 1 second or longer.

References

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