Case IH 520192-04 - UCM – UCM: Primary Wheel Angle Sensor Voltage Below Normal

The analog input signal from the Primary Wheel Angle Sensor is detecting a voltage that is below normal (typically indicating a short to ground or an open circuit). The sensor provides the steering angle position to the control system; when the voltage drops below the acceptable threshold, the system cannot determine the wheel position, which will disable auto-guidance (AccuGuide) and automated steering functions.

• MAGNUM AFS Connect
• Maxxum 110
• Maxxum 115
• Maxxum 120
• Maxxum 125
• Maxxum 130
• Maxxum 140
• Puma
• Magnum
• Patriot 3230
• Patriot 3320
• Patriot 3330
• Patriot 4420
• Patriot 4430
• Trident 5550
• 2000-series Early Riser Planters
• 2160
• 7120

1. 1

   Inspect the 3-pin wiring harness connecting the wheel angle sensor to the UCM for chafing, breaks, or areas where the wire might be shorted to the chassis (ground).

2. 2

   Disconnect the sensor and use a multimeter to verify that the UCM is supplying the correct reference voltage (typically 5V) and a solid ground to the connector.

3. 3

   Test the signal wire for continuity from the sensor connector back to the UCM pins.

4. 4

   Inspect the sensor's physical linkage arm and tie-rod connection. Ensure the arm is not bent, disconnected, or suffering from excessive mechanical play, which can push the sensor out of its calibrated voltage range.

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent electrical spikes during the repair.

2. 2

   Locate the Sensor

   Locate the primary wheel angle sensor on the steering axle (typically mounted near the steering cylinder or right-hand subframe).

3. 3

   Disconnect Wiring

   Unplug the 3-pin weatherproof connector from the sensor.

4. 4

   Remove Linkage

   Unbolt the sensor linkage arm from the steering cylinder or tie-rod.

5. 5

   Remove Sensor

   Remove the retaining hardware (screws/O-rings) holding the sensor body to the mounting bracket and remove the faulty sensor.

6. 6

   Install New Sensor

   Mount the new wheel angle sensor and secure the retaining hardware. Reattach the linkage arm, ensuring it has a full range of motion without binding.

7. 7

   Reconnect Wiring

   Plug the 3-pin electrical harness back into the sensor.

8. 8

   Calibration

   Power on the tractor and navigate to the ISObus diagnostic page on the Pro 700 or Pro 1200 display. You must perform a Wheel Angle Sensor and Steering Valve calibration so the UCM can learn the new sensor's center, full-left, and full-right voltage limits.