Case IH 2628 – ZTC: Transmission output shaft speed sensor (N_Ab2) open circuit or shorted to power

The transmission controller is not receiving a valid signal from the N_Ab2 sensor because the electrical circuit is either broken (disconnected/cut wire or internally failed sensor) or the signal wire is shorted to a voltage source. Without this signal, the transmission computer loses precision control over gear speeds and shifting.

• Steiger T4B
• Magnum series (180, 200, 225, 250, 340, 7110-8950 series)
• Puma CVX
• Maxxum CVX

1. 1

   Disconnect the battery terminals (negative first) before working on the electrical systems to prevent damage.

2. 2

   Inspect the wiring harness running from the ZTC module to the N_Ab2 transmission output speed sensor for chafing, cuts, or melted insulation that could cause a short to power or an open circuit.

3. 3

   Unplug the sensor and check the connector pins for corrosion, moisture, or pushed-out pins.

4. 4

   Use a multimeter to check for continuity on the sensor signal and ground wires back to the ZTC. Test the signal wire for unwanted voltage (short to power).

5. 5

   Test the sensor itself for an internal open circuit by measuring its resistance.

1. 1

   Preparation

   Park the machine on a level surface, engage the parking brake, turn off the engine, and allow the transmission oil to cool down. Disconnect the battery.

2. 2

   Locate the Sensor

   Locate the N_Ab2 transmission output speed sensor on the exterior of the ZF transmission housing.

3. 3

   Removal

   Disconnect the electrical harness connector from the sensor. Remove the retaining bolt securing the sensor to the housing.

4. 4

   Extraction

   Carefully pull the old speed sensor straight out of the transmission case.

5. 5

   Installation

   Lubricate the O-ring on the new sensor with clean transmission fluid to prevent tearing. Push the new sensor into the port and install the retaining bolt.

6. 6

   Reassembly

   Reconnect the electrical connector, ensuring the weather seal is intact to keep moisture and debris out.

7. 7

   Testing

   Reconnect the battery, clear the fault codes from the ZTC, and test drive the tractor to ensure the transmission shifts smoothly and the speed-related error codes do not return.