Case IH 2579 (3825.01) - DEC – UCM (Universal Control Module) or Transmission Control Module: Wheel speed (transmission output speed) sensor #2 - critical air gap

The control module determines that the signal from the transmission output speed sensor #2 is erratic, intermittent, or incorrect. The most common physical cause is that the physical air gap between the magnetic speed sensor and the transmission gear teeth has become too wide, resulting in a weak or dropped signal.

• MAXXUM T4E
• Magnum 275
• Magnum 180
• Puma series
• Steiger/Quadtrac models
• Axial-Flow 7230
• Axial-Flow 8230
• Axial-Flow 9230
• T7.175
• T7.190
• T7.210
• T7.270

1. 1

   Check for related transmission codes (such as Trans Fault 81, 3020, or 56004) to rule out other input speed faults

2. 2

   Disconnect the transmission output speed sensor and measure its resistance (should be approximately 3.5k Ohms at room temperature)

3. 3

   Inspect the sensor connector and transmission harness for corrosion, open circuits, or shorts to ground/12V

4. 4

   Check the physical air gap distance between the tip of the speed sensor and the gear

1. 1

   Access the Sensor

   Locate Transmission Output Speed Sensor #2 on the transmission housing.

2. 2

   Adjust the Air Gap

   If the sensor passes the resistance test, the air gap is likely the culprit. Adjust the depth of the sensor. Note: In some cases, technicians have had to machine the sensor mounting surface slightly to allow the sensor to sit deeper and close the air gap.

3. 3

   Replace the Sensor

   If the sensor fails the resistance test (reads open or shorted) or is physically damaged, remove it and install a new sensor. Ensure the O-ring/seal is replaced simultaneously to prevent hydraulic leaks.

4. 4

   Clear and Test

   Once the cause of the error code has been rectified, use the diagnostic interface to clear the error code and test drive the tractor in multiple gears to ensure the transmission control module receives a valid speed signal above the dropout level.