Case IH NH2077 – TCU: Flywheel Speed Sensor Short Circuit

The transmission control unit has detected an electrical short circuit in the flywheel speed sensor circuit. This can be caused by an internal fault within the sensor itself or by damage to the wiring harness connecting the sensor to the control module. A short circuit disrupts the speed signal, leading to incorrect speed readings or a complete loss of signal, which can negatively affect automatic gear shifting and the accuracy of the RPM display on the dashboard.

• Puma 130
• Puma 140
• Puma 145
• Puma 150
• Puma 160
• Puma 165
• Puma 170
• Puma 180
• Puma 185
• Puma 195
• Puma 200
• Puma 210
• Puma 215
• Puma 220
• Puma 225
• Puma 240
• Maxxum 110
• Maxxum 115
• Maxxum 120
• Maxxum 125
• Maxxum 130
• Maxxum 135
• Maxxum 140
• Maxxum 145
• Maxxum 150
• MXU100
• MXU110
• MXU115
• MXU125
• MXU130
• MXU135

1. 1

   Visually inspect the wiring harness leading to the flywheel speed sensor for physical damage, chafing, melting, or corrosion on the connector pins. The sensor is typically located on the engine or transmission housing, near the flywheel.

2. 2

   Check for power and ground: Disconnect the sensor's electrical connector. With the key 'ON', use a multimeter to verify the harness-side connector has the correct voltage (typically 5V or 12V) on the power pin and continuity to ground on the ground pin.

3. 3

   Check the signal wire: With the sensor disconnected and the key 'ON', check for voltage on the signal wire (should be near 0V). Verify there is no continuity (an open circuit) between the signal wire and the ground wire in the harness.

1. 1

   Repair wiring harness

   If diagnostic checks reveal a short circuit in the wiring harness, repair or replace the damaged section of wiring.

2. 2

   Remove faulty sensor

   If the wiring is intact, the sensor is likely faulty. Disconnect the negative battery terminal and the electrical connector from the old flywheel speed sensor. Remove the retaining screw or bolt and carefully detach the sensor from its mounting on the engine or transmission housing.

3. 3

   Install new sensor

   Install the new sensor, ensuring it is properly seated. If applicable, set the air gap between the sensor and the flywheel to the specification of 0.015 to 0.025 inches.

4. 4

   Reconnect and verify

   Reconnect the electrical connector and the battery terminal. Clear the fault codes from the transmission controller using a diagnostic tool or by cycling the key. Start the tractor and verify that the fault code does not reappear and that the tachometer is functioning correctly.