Case IH 2635 – ZTC: Implausible reading between the two hydrostatic unit speed sensors: number of teeth N_Hyd2 is less than N_Hyd1

The controller detects a mismatch where the pulse count from N_Hyd2 is lower than N_Hyd1. This is typically caused by a failing sensor dropping the signal, metal shavings on the sensor's magnetic tip distorting the reading, a wiring harness issue, or physical damage to the internal tone ring/gear.

• Steiger T4B
• Case IH Magnum CVT series (e.g., 220, 250, 340, 380 CVT)
• Case IH Steiger CVT series
• Case IH Puma CVX series
• Case IH Optum CVX / Maxxum CVX

1. 1

   Inspect the wiring harness and connectors leading to the N_Hyd1 and N_Hyd2 speed sensors for chafed wires, short circuits to ground/power, or corrosion in the pins.

2. 2

   Remove both hydrostatic speed sensors and inspect their magnetic tips for accumulated metal shavings that could distort the reading.

3. 3

   Check the transmission fluid and filter for heavy metal contamination, which could indicate a mechanical failure of the hydrostatic unit or tone ring.

4. 4

   Test the resistance and signal output of the sensors while the machine is running (if possible) to isolate whether the sensor is dead or the harness is dropping the voltage.

1. 1

   Prep the Machine

   Park the tractor on a level surface, engage the parking brake, turn off the engine, and disconnect the battery to protect the ZTC module.

2. 2

   Locate the Sensors

   Locate the N_Hyd1 and N_Hyd2 speed sensors on the exterior of the transmission's hydrostatic module.

3. 3

   Remove the Sensor

   Disconnect the electrical connector. Remove the retaining bolt holding the faulty sensor in the transmission housing and pull the sensor straight out.

4. 4

   Clean or Replace

   If the sensor is heavily coated in metallic sludge, clean it, reinstall, and re-test. If the sensor has failed internally, discard it and prepare the new sensor.

5. 5

   Install New Sensor

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

6. 6

   Reconnect & Reassemble

   Reconnect the wiring harness, ensuring the weather seal clicks into place. Reconnect the battery.

7. 7

   Calibration

   Connect the Case IH EST (Electronic Service Tool) or use the AFS Pro monitor to clear the 2635 fault code. You must perform a CVT transmission calibration so the ZTC can relearn the hydrostatic unit's sensor parameters.