Eaton Fuller Advantage (2017) Fault Code: 72 PID: SPN: 772 FMI: 7 Failed to Select Rail: Mechanical System Not Responding

Overview:
The Fuller Advantage transmission uses the X-Y Shifter to engage and disengage a gear based on the driver’s selected mode of operation. Rail selection is achieved by activating the X-Y Shifter Rail Motor, which controls the lateral movement of the X-Y Shift Finger within the Shift Bar Housing. Certain shifts require the transmission to engage a different rail on the Shift Bar Housing. These rail shifts require the X-Y Shifter to move to Neutral prior to selecting another rail and allowing the next gear engagement. The Shift Bar Housing Interlock physically prevents the engagement of two gears at the same time.

Fault Code 72 sets when the X-Y Shift Finger attempts to move to a different rail position, but the X-Y Rail Position Sensor indicates that the transmission was unable to select the next rail position. Transmission Electronic Control Unit (TECU) detected a system failure, but was unable to detect the specific root cause.

Detection:
This fault can only be detected when there are no failures of the TECU, X-Y Gear or Rail Motors, X-Y Position Sensors or Battery Supply voltage. This fault code is set when the system is unable to move to a different rail position and the transmission is not engaged in a gear.

Conditions to Set Fault Code Active:
FMI 7 – Mechanical System Not Responding: After being unable to select a rail position for 2 seconds, the fault code sets Active.

Fallback:
FMI 7:
• Transmission may not be able to complete a shift to the proper rail.
• Transmission will attempt to move the Shift Finger to the proper rail.
• Gear display may flash current or destination gear.

Conditions to Set Fault Code Inactive:
FMI 7: The system successfully positions the Shift Finger on the proper rail.

Possible Causes:
FMI 7:
1) Vehicle Power Supply
– Poor power or ground supply to TECU
– Bent, spread, corroded or loose terminals
2) Vehicle Batteries
– Internal failure
3) Transmission Harness
– Damaged wiring between the TECU and X-Y Shifter
– Bent, spread, corroded or loose terminals
4) X-Y Shifter
– Worn or damaged X-Y Shifter ball screw, center shaft bushing, or other internal components
– Contaminated X-Y Shifter ball screw due to coolant leak or oil contamination
– Bent, spread, corroded or loose terminals
5) Mechanical Transmission
– Worn or damaged Shift Bar Housing
– Worn Sliding Clutch slot width
– Worn or damaged Shift Yokes
– Worn or damaged internal transmission components