Eaton Fuller Advantage (2017) Fault Code: 56 PID: 161 SPN: FMI: 5 Input Shaft Speed Sensor: Current Below Normal or Open Circuit

Overview
The Fuller Advantage transmission is equipped with electronic speed sensors. The Input Shaft, Main Shaft and Output Shaft Speed Sensors are used to calculate gear ratios within the transmission. The Input Shaft Speed Sensor measures the rotational speed of the Input Shaft, taken from the upper countershaft drive gear. The Main Shaft Speed Sensor measures the rotational speed of the transmission gearing exiting the main case, taken from the auxiliary upper countershaft gear. The Output Shaft Speed Sensor measures the rotational speed of the output shaft taken from the Output Shaft Tone Wheel. The Transmission Electronic Control Unit (TECU) compares these speeds to calculate the gear ratios of the main case, auxiliary case and overall transmission.

The Input Shaft Speed Sensor transmits a voltage signal to the TECU based on the rotational speed of the Input Shaft entering the transmission main case. The TECU compares Input Shaft Speed to Main Shaft Speed to confirm the gear ratio of the main case and compares Input Shaft Speed to Output Shaft Speed to confirm the overall transmission gear ratio.

Fault Code 56 indicates an electrical fault within the Input Shaft Speed Sensor circuit or a speed value that is inconsistent with the calculated gear ratios.

Detection:
The TECU monitors the Input Shaft Speed Sensor signal and compares the sensor readings with the Main Shaft Speed Sensor and the Output Shaft Speed Sensor to determine sensor validity. The TECU also monitors the Input Shaft Speed Sensor electrical circuit for any shorts to power, ground or open circuits.

Conditions to Set Fault Code Active:
The system can detect Input Shaft Speed Sensor faults when one of the following conditions is present for 1 second or longer:
FMI 5 – Current Below Normal or Open Circuit: TECU detects an open circuit or the Input Shaft Speed Sensor has high resistance.

Fallback:
All FMIs
• “F” flashes in gear display.
• Service light flashes (if equipped).
• Transmission will not engage a gear from neutral.
• Transmission may be limited to down shifts only.
• Transmission operates as normal until neutral gear selection is attained. Once in neutral, the transmission will not engage a start gear.

Conditions to Set Fault Code Inactive:
All FMIs: TECU receives a valid signal from the Input Shaft Speed Sensor and detects no electrical open or short circuits for 2 seconds.

Possible Causes:
All FMIs
1) Transmission Harness
– Bent, spread, corroded or loose terminals
– Wiring shorted to ground, shorted to power or open
2) Input Shaft Speed Sensor
– Internal failure
– Physical damage
3) Mechanical Transmission
– Internal transmission wear or damage