Case IH 191-02 - DEC – Transmission Controller: Transmission Output Speed Sensor data is erratic, intermittent, or incorrect

The transmission controller is receiving a fluctuating, dropping, or implausible signal from the transmission output speed sensor. Because the controller relies on this sensor to determine ground speed and manage shifting, this condition typically results in the transmission failing to shift correctly, dropping out of gear, or defaulting to a limp mode.

• MAGNUM AFS Connect
• Magnum 180
• Magnum 190
• Magnum 210
• Magnum 225
• Magnum 235
• Magnum 240
• Magnum 260
• Magnum 290
• Magnum 315
• Magnum 340
• Magnum 370
• Puma 140
• Puma 150
• Puma 165
• Puma 170
• Puma 180
• Puma 185
• Puma 195
• Puma 200
• Puma 210
• Puma 220
• Puma 230
• Puma 240
• Steiger 420
• Steiger 470
• Quadtrac 420
• Quadtrac 470
• Farmall 95U
• Farmall 105U
• Farmall 115U Pro EP

1. 1

   Connect the electronic service tool, select 'inst trans output speed', and monitor the sensor output in RPM while driving to verify if the signal is dropping out or spiking.

2. 2

   Inspect the sensor's wiring harness (e.g., Connector X-309 or CN3B) for loose pins, corrosion, or physical damage.

3. 3

   With the engine off, use a multimeter to check the sensor circuit for a short to ground, short to power (12V/Vcc), or an open circuit.

4. 4

   Remove the sensor and inspect the magnetic tip for metal shavings or heavy debris that can cause erratic readings.

1. 1

   Park the tractor on a level surface, engage the parking brake, and turn off the engine.

2. 2

   Locate the transmission output speed sensor.

   On many CVT models, it is located on the hydrostatic pump cover assembly on the transmission housing; on others, it is located on the rear axle housing.

3. 3

   Thoroughly clean the area around the sensor to prevent dirt from falling into the transmission housing.

4. 4

   Disconnect the electrical wire harness from the sensor.

5. 5

   Remove the retaining hardware securing the sensor.

   Typically an M6 or M8 hex socket screw.

6. 6

   Carefully pull the sensor straight out of the housing.

   Have a rag ready to catch any minor fluid seepage.

7. 7

   Lubricate the O-ring on the new sensor with clean transmission/hydraulic fluid.

8. 8

   Insert the new sensor into the port, ensuring it seats fully.

9. 9

   Install and tighten the retaining hex screw to the specified torque.

10. 10

    Reconnect the electrical harness.

11. 11

    Clear the fault codes using the diagnostic tool and test drive the tractor to verify smooth shifting and a stable RPM reading.