Eaton Fuller Advantage (2017) Fault Code: 73 PID: SPN: 781 FMI: 7 Failed to Engage Gear: 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. Gear engagement is achieved by activating the X-Y Shifter Gear Motor, which controls the fore-and-aft movement of the Shift Finger. Pushing the Shift Finger against one of the Shift Bar Housing Shift Blocks guides the Shift Yoke to engage the Sliding Clutch into a gear. The position of the X-Y Shift Finger is monitored by the Transmission Electronic Control Unit (TECU) by way of the X-Y Gear Position and Rail Position Sensors.

Fault Code 73 is set when the X-Y Shift Finger attempts to engage a gear, but the X-Y Gear Position Sensor indicates that the transmission was unable to engage that gear. The 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 engage a gear.

Conditions to Set Fault Code Active:
FMI 7 – Mechanical System Not Responding: If the X-Y Gear Position Sensor does not meet the minimum gear engagement value after five consecutive attempts to engage the desired gear, this fault code sets Active.

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

Conditions to Set Fault Code Inactive:
FMI 7: The system successfully engages the desired gear.

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 component