Case IH 2155 (519170.04) - DEC – Transmission Control Unit (TCU) or the main Drivetrain/Chassis Controller: Synchro 1-3 Position Sensor - open circuit or short circuit to GND

The fault indicates a critical electrical failure in the circuit for the "Synchro 1-3 Position Sensor." Open Circuit: The control module is not detecting any voltage or signal from the sensor, usually caused by a broken wire, a disconnected plug, or a completely failed internal sensor element. Short Circuit to GND (Ground): The signal wire is chafed or pinched and is touching the machine's chassis (ground) or the ground wire, pulling the sensor's signal voltage down to 0V. Because the controller cannot determine the physical position of the 1-3 synchronizer, it will likely disable shifting into those specific ranges to prevent mechanical transmission damage.

• MAXXUM T4E
• Maxxum
• Puma
• Magnum

1. 1

   Visually inspect the wiring harness leading to the transmission housing for pinched wires, rodent damage, or chafing against the transmission casing.

2. 2

   Disconnect the sensor and check the pins on both the sensor side and the harness side for corrosion, bent pins, or moisture ingress.

3. 3

   Perform a voltage test by turning the key to the ON position (engine off) and probing the harness connector to verify a 5V reference signal and a good ground.

4. 4

   With the battery disconnected, test the signal wire for continuity back to the TCU harness and for continuity to ground to identify any short circuits.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the negative battery terminal to protect the TCU.

2. 2

   Isolate the Fault

   If the diagnostic checks reveal a wiring issue (short to ground or broken wire), repair the wiring harness using OEM-approved weather-sealed connectors or replace the affected harness section.

3. 3

   Replace the Sensor (if wiring is intact)

   If the harness provides the correct 5V reference and ground, but the fault persists, the sensor itself has failed internally.

4. 4

   Remove the Sensor

   Clean the area around the sensor on the transmission housing to prevent dirt from entering the gearbox. Remove the retaining bolt(s) and pull the sensor out.

5. 5

   Install the New Sensor

   Lubricate the O-ring on the new sensor with clean transmission fluid. Insert it into the housing and torque the retaining bolt to OEM specifications.

6. 6

   Reassemble and Clear Codes

   Reconnect the battery. Turn the key ON and use the tractor's AFS Pro display or a diagnostic tool to clear the inactive fault codes.

7. 7

   Calibration

   A new transmission position sensor will almost certainly require a transmission calibration routine to be run via the tractor's display or dealer software so the TCU can learn the physical end-stops of the 1-3 synchronizer.