Case IH 12636 – Transmission Controller (TRANS / DCU) or Instrumentation Controller: Rear left wheel speed sensor - wheel diameter incorrect

The control module is detecting a mismatch between the physical speed signal coming from the rear left wheel speed sensor and the expected speed based on the programmed wheel diameter (pulse provider) stored in the system's parameters. This can be caused by an incorrectly programmed wheel size in the cab monitor, a faulty wheel speed sensor dropping voltage, or a damaged sensor harness.

• Magnum
• Steiger
• MX/TG series

1. 1

   Verify Programmed Wheel Diameter: Access the tractor's instrumentation controller or cab monitor calibration menu to ensure the programmed wheel diameter matches the physical rear tires installed on the machine.

2. 2

   Inspect the Sensor Harness: Check the wiring harness leading to the rear left wheel speed sensor for breaks, shorts to ground, or poor connections.

3. 3

   Test Sensor Output: Monitor the sensor's output voltage. A failing Hall-effect wheel speed sensor may drop its output voltage (e.g., from a baseline 5V down to 2.8V), which the ECU interprets as an invalid or missing signal.

1. 1

   Calibrate the System

   Enter the calibration mode on the cab monitor. Select the 'PLUS' or 'MINUS' key to adjust the wheel diameter setting until the correct value is achieved, then press the center key to confirm. Test drive the tractor to see if the fault clears.

2. 2

   Access the Sensor

   If the calibration is correct but the fault persists, locate the rear left wheel speed sensor (typically mounted on the rear axle housing or final drive).

3. 3

   Remove the Sensor

   Disconnect the sensor's electrical pigtail connector. Remove the retaining bolt(s) holding the sensor in place and pull the sensor out of the housing.

4. 4

   Install the New Sensor

   Lubricate the O-ring on the new wheel speed sensor, insert it into the mounting hole, and torque the retaining bolt to OEM specifications.

5. 5

   Reconnect and Clear Codes

   Reconnect the wiring harness, turn the key switch to the ON position, and use the instrumentation controller to clear the active transmission/speed faults.