Eaton Fuller Hybrid Transmission Fault Code 72 – Failed to Select Rail

Fault code for Eaton Hybrid Drive Systems models (MY08) EH-8E306A-U, EH-8E306A-UPG, EH-8E306A-UP, EH-8E306A-CD, EH-8E306A-T, EH-6E606B-CD, (MY09) EH-8E406A-U/P, EH-8E406A-UP, EH-8E406A-UPG, EH-8E406A-CD, EH-8E406A-CDG, EH-8E406A-CDR, EH-8E406A-T, EH-6E706B-CD, EH-6E706B-P and EH-6E706B-UPG. Read below to learn how to test, clear and fix fault code errors for your Freightliner, Mack, Peterbilt, Kenworth, Volvo, International, and heavy-duty truck and equipment. The Transmission Electronic Control Unit controls the Electric Shifter, which engages the different rails and gear positions. The Electric Shifter is comprised of two electric motors; one changes the rail position and the other changes the gear position.

Fault Code 72 – Failed to Select Rail Detection

The following preconditions must be met before the system detects the fault:

  • TECU ignition voltage is greater than 7 volts and less than 16 volts.
  • TECU System Battery Voltage Low Fault is Inactive.
  • TECU System Battery Voltage Weak Fault is Inactive.
  • This fault may occur at power up after 15 seconds.

Note: When troubleshooting an Inactive code refer to the Product Diagnostic Mode (PDM)

Conditions to Set Fault Code Active

  • FMI 7 is set when the Electric Shifter fails five consecutive attempts to engage a particular rail position.

Fallback When Fault Code 72 is set the following conditions occur:

  • Fault is stored in TECU memory.
  • If the fault sets while driving, the vehicle continues to select the proper rail position.

Conditions to Set Fault Code Inactive

Only Inactive faults can be cleared from the Transmission Electronic Control Unit (TECU) or HCM history using ServiceRanger. The TECU automatically clears the faults from history after 200 hours and the HCM automatically clears the faults from history after the fault has been Inactive for 200 hours.

This fault code can be caused by any of the following:

  • FMI 7
    • Shift Bar Housing
    • Electric Shifter
    • Rail Select Sensor
    • TECU

Fault Code 72 – Failed to Select Rail Test

Component Identification:

Shift Forks Eaton Fuller transmission

The picture above shows the Shift Forks in the neutral position.

NOTE: Refer to the Eaton Hybrid Component and Connector Location for Connector Locations in MY08 Systems

NOTE: Refer to the Eaton Hybrid Component and Connector Location for Connector Locations in MY09 Systems.

STEP 1. Verify gear display in neutral gear position.

  1.  Retrieve Active fault codes and FMIs with ServiceRanger using the 9-Way Diagnostic Connector or manually.
  2. Key on.
  3. Place Shift Device in neutral.
  4. Press Service Brake.
  5. Select Drive.
  6. Observe gear display:
    • If there is an Active Fault Code 72, go to Step 2.
    • If Gear Display shows solid gear, go to Step 5.

STEP 2. Perform Electrical Pretest.

  1. Perform the Electrical Pretest.
    • If no issues found during the Electrical Pretest, go to Step 3.
    • If issue was repaired during the Electrical Pretest, go to Step 1.

STEP 3. Verify integrity of Shift Bar Housing components.

  1.  Key off.
  2. Remove Electric Shifter* from Shift Bar Housing.
  3. Inspect the following:
    • Shift Blocks are fastened to Shift Rails securely
    • Shift Rails move into each gear position
    • Electric Shifter is free from any excessive lube contamination buildup
    • Two gear positions can not be engaged at the same time
      • If no problem found, replace the Electric Shifter, then go to Step 4.
      • If problem is found, repair as required, then go to Step 4.

STEP 4. Verify repair.

  1. Key off.
  2. Reconnect all connectors and the negative battery cable.
  3.  Key on.
  4. Clear codes, see  Clear Inactive Faults.
  5. Drive the vehicle and attempt to reset the code.
  6. Check for codes, see View Active and Inactive Faults.
    • If no codes, test is complete.
    • If fault Code 72 appears, find error in testing, go to Step 1.
    • If a code other than 72 appears, see Fault Code Index List.

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