Case IH 2681 – Transmission Control Unit (TCU) or Vehicle/Tractor Control Unit: Transmission Input Shaft Speed Sensor - measured speed is higher than limit

The control module is receiving an RPM signal from the transmission input shaft speed sensor that exceeds the maximum programmed threshold for the current gear or engine speed. This can be caused by a failing sensor sending erratic/spiked signals, a short circuit in the sensor wiring, or excessive metal debris accumulating on the sensor's magnetic tip.

• Steiger T4B
• Case IH Steiger / Quadtrac series (e.g., 535 Quadtrac)
• Case IH Magnum series
• Case IH Maxxum series (e.g., MX150, MX170)

1. 1

   Perform a resistance test on the sensor (should measure around 3000 ohms; open or zero indicates a dead sensor)

2. 2

   Inspect the wiring harness from the sensor to the transmission controller for rubbed-through insulation or pinched wires causing a short circuit

3. 3

   Remove the sensor and inspect the magnetic tip for metal dust accumulation; clean the tip and reinstall to see if the code clears

4. 4

   Use the CNH Electronic Service Tool (EST) to monitor live data for Sensor 1 (Input Shaft Speed) for erratic RPM jumps

1. 1

   Locate the Sensor

   The input shaft speed sensor (often designated as Sensor 1) is typically located on the top or upper side of the transmission housing, near the bell housing/input shaft area.

2. 2

   Clean the Area

   Thoroughly clean the area around the sensor to prevent dirt from falling into the transmission housing.

3. 3

   Remove the Sensor

   Disconnect the electrical connector. Remove the retaining bolt and carefully pull the sensor straight out.

4. 4

   Inspect for Damage

   Check the sensor tip for physical damage. If the tip is smashed, there may be catastrophic internal transmission bearing or shaft failure.

5. 5

   Install the New Sensor

   Lubricate the O-ring on the new sensor with clean transmission hydraulic fluid. Insert the sensor into the port.

6. 6

   Secure and Reconnect

   Install the retaining bolt and torque to OEM specifications. Reconnect the electrical harness.

7. 7

   Clear Codes and Calibrate

   Use the CNH Electronic Service Tool (EST) to clear the 2681 fault code. Depending on the model, a transmission calibration routine may need to be run so the TCU can relearn the clutch fill times and sensor baselines.