Eaton Fuller Advantage (2017) Fault Code: 81 PID: SPN: 780 FMI: 7 Gear Engagement Detected: Mechanical System Not Responding

Overview:
The Fuller Advantage transmission uses the X-Y Shifter to engage and disengage gears based on the driver’s selected mode of operation. Gear engagement and disengagement 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 or disengage the Sliding Clutch into or out of a gear. The position of the X-Y Shift Finger is controlled and monitored by the Transmission Electronic Control Unit (TECU) by way of the X-Y Gear Position and Rail Position Sensors. The TECU uses the Transmission Speed Sensors to verify gear engagement or disengagement, and to confirm that the current transmission gear ratio is appropriate for the selected gear.

Fault Code 81 is set when the X-Y Gear Position Sensor and Rail Position Sensor indicate that the Shift Finger is in a neutral position, but other indicators do not confirm that the transmission is in Neutral.

Detection:
This fault can only be detected when there are no failures of the TECU, X-Y Position Sensors or Transmission Speed Sensors. This fault code is set when the Transmission Speed Sensor values are not consistent with the X-Y Gear Position and Rail Position values.

Conditions to Set Fault Code Active:
FMI 7 – Mechanical System Not Responding: This fault sets in one of two ways:
• Both the X-Y Gear Position Sensor and Rail Position Sensor indicate the Shift Finger is in a neutral position. However, the Transmission Speed Sensors indicate that the transmission is in gear. If the overall transmission gear ratio indicates the transmission is not in neutral after two unsuccessful attempts to pull the Shift Finger to neutral, the fault sets Active.
• Vehicle is stationary and the transmission is in neutral. Three seconds after releasing the brake pedal, the clutch begins to close. If the engine begins to stall as the clutch closes, the system will set the fault Active due to the possibility that the transmission is improperly engaged in a gear.

Fallback:
FMI 7
• “F” flashes in gear display.
• Service light flashes (if equipped).
• Transmission may remain in current gear.
• Engine may have to be shut down with transmission still in gear.

Conditions to Set Fault Code Inactive:
FMI 7: This fault code sets Inactive in one of two ways:
• Ignition key is turned off and TECU is powered down.
• The system successfully engages the desired gear.

Possible Causes:
FMI 7
1) X-Y Shifter
– Bent, spread, corroded or loose terminals
– Wiring shorted to ground, shorted to power or open
– Gear Position Sensor damaged
– Worn or damaged X-Y Shifter ball screw, center shaft bushing, or other internal components
2) Transmission Harness
– Bent, spread, corroded or loose terminals
– Wiring shorted to ground, shorted to power or open
3) Mechanical Transmission
– Worn or damaged Shift Bar Housing
– Worn Sliding Clutch slot width
– Worn or damaged Shift Yokes
– Worn or damaged internal transmission components