Case IH 12639 – ABS Module / Transmission/Vehicle Control Module (TECU): Front right wheel speed sensor - wheel diameter incorrect

This fault code indicates a mismatch between the speed reading from the front right wheel speed sensor and the expected speed based on the programmed wheel diameter. The underlying condition is typically caused by an incorrect wheel diameter parameter programmed into the controller, mismatched tire sizes, or an erratic signal from the front right wheel speed sensor causing the system to calculate an impossible wheel speed ratio.

• Case IH Puma Series (Puma 170, 185, 200, 215, 230)

1. 1

   Verify Tire Sizes: Physically check the front right tire size and compare it to the other tires on the machine. Ensure they match and are inflated to the correct rolling circumference.

2. 2

   Check ECU Parameters: Connect the CNH Electronic Service Tool (EST) laptop to the tractor. Navigate to the transmission/ABS controller parameters and verify that the programmed 'Wheel Diameter' or 'Rolling Radius' matches the physical tires installed on the tractor.

3. 3

   Monitor Sensor Output: Using the EST, monitor the 'Transmission Local Engine Speed' and 'Transmission Output Shaft Speed' or individual wheel speeds while driving. Look for erratic readings or dropouts from the front right wheel speed sensor.

4. 4

   Inspect Wiring and Sensor Gap: Inspect the wiring harness leading to the front right wheel speed sensor (Circuit 9615 / 9616) for chafing, open circuits, or shorts to ground. Check the sensor mounting for debris, looseness, or an improper air gap between the sensor and the tone ring.

1. 1

   Reprogram Wheel Diameter

   If the EST shows an incorrect wheel diameter parameter, reprogram the ECU with the correct value for the installed tires. Clear the fault code and test drive.

2. 2

   Clean the Sensor/Tone Ring

   If the parameter is correct but the signal is erratic, safely support the front right axle. Remove the wheel speed sensor, clean any metallic debris from the magnetic tip, and inspect the tone ring through the mounting hole for damage or packed mud.

3. 3

   Replace the Sensor

   If the wiring harness tests good (continuity from the sensor connector back to the ABS/TECU pins) but the sensor fails to produce a steady signal, replace the front right wheel speed sensor.

4. 4

   Recalibrate and Test

   After replacing the sensor, clear the fault codes using the EST. Operate the tractor at various ground speeds to ensure the controller reads the proper ratio and the fault code does not return.