Case IH 2627 – Transmission Control Unit (TCU) / ZTC: Hydrostatic unit speed sensor (N_Hyd1) open circuit or shorted to power

The N_Hyd1 sensor monitors the rotational speed of the hydrostatic pump/motor unit. When this circuit is open or shorted to power, the controller loses this critical speed signal, which typically forces the transmission into an emergency operating mode or causes erratic shifting.

• Steiger T4B
• Case IH CVX series
• Case IH Puma CVX
• Case IH Maxxum CVX
• Case IH Optum CVT

1. 1

   Inspect the wiring harness running from the ZTC (Transmission Controller) to the N_Hyd1 speed sensor on the hydrostatic unit for chafed wires, melted insulation, or pinch points.

2. 2

   Disconnect the N_Hyd1 sensor and check the connector pins for corrosion, pushed-back pins, or transmission fluid ingress, which can cause a short.

3. 3

   Using a multimeter, check for continuity on the signal and ground wires between the sensor connector and the ZTC harness connector to rule out an open circuit.

4. 4

   With the key ON (engine OFF), probe the sensor's signal and ground wires on the harness side to ensure there is no unintended voltage present (short to power).

5. 5

   Measure the internal resistance of the N_Hyd1 sensor and compare it to OEM specifications. An infinite reading indicates an internal open circuit in the sensor itself.

1. 1

   Preparation

   Park the tractor on a smooth, level surface, engage the parking brake, and turn off the engine. Disconnect the negative battery terminal.

2. 2

   Locate the Sensor

   Locate the N_Hyd1 speed sensor on the exterior of the transmission's hydrostatic unit.

3. 3

   Removal

   Disconnect the electrical connector from the sensor. Remove the mounting screw/bolt securing the sensor to the housing.

4. 4

   Extraction

   Carefully pull the old speed sensor straight out of the transmission housing. Have a rag ready, as a small amount of transmission fluid may weep from the port.

5. 5

   Installation

   Lubricate the O-ring on the new sensor with clean transmission fluid. Insert the new sensor into the port until it is fully seated.

6. 6

   Torque

   Install the mounting screw and tighten it to the OEM specification (standard torque for ZF hydrostatic unit speed sensors is typically 9.5 Nm).

7. 7

   Reassembly

   Reconnect the electrical connector, ensuring it clicks into place. Reconnect the battery.

8. 8

   Calibration/Clearing

   Use a diagnostic service tool to clear the 2627 fault code from the ZTC. Perform a test drive to verify that the transmission shifts smoothly and the code does not return.