Case IH 15218 – Steering Valve Controller: Primary wheel angle sensor (AD1) - short circuit to a source greater than 4.9V

The steering valve controller is receiving a signal voltage from the primary wheel angle sensor (AD1) that is abnormally high (greater than 4.9 volts). This typically means the sensor's signal wire is shorted to a 5V reference or battery voltage, or the sensor has failed internally and is passing the full reference voltage to the signal return.

• Steiger T4B
• Case IH Farmall 40, 45, and 50 Tractors (with Cab and CVT Transmission)
• Case IH Steiger and STX Series Tractors (e.g., 280-600 HP models)
• Case IH Magnum and Maxxum Series
• Case IH Puma Series
• Case IH Patriot Sprayers (3230, 3320, 3330, 4420, 4430)
• Case G-Series Wheel Loaders (Articulation angle sensor applications)

1. 1

   Visually inspect the primary wheel angle sensor (located on the steering axle or articulation joint) and its linkage for physical damage.

2. 2

   Trace the wiring harness from the sensor back to the steering valve controller. Look for chafed wires, pinched harnesses, or melted insulation that could cause the signal wire to short to a power wire.

3. 3

   Disconnect the sensor, turn the key ON, and measure the voltage at the signal pin on the harness side. If it reads >4.9V with the sensor unplugged, the wiring harness is shorted to power. If the voltage drops to 0V, the short is likely internal to the sensor.

4. 4

   Verify that the sensor is receiving a clean 5V reference and has a solid ground connection. A lost ground can sometimes cause the signal voltage to float high.

1. 1

   Secure the Machine

   Park the machine on a level surface, turn off the engine, and ensure the steering mechanism cannot move suddenly, as working around the wheel angle sensor can cause severe injury if the steering actuates.

2. 2

   Disconnect the Battery

   Disconnect battery power to prevent electrical spikes during repair.

3. 3

   Remove the Sensor

   Disconnect the electrical connector from the wheel angle sensor. Remove the retaining ring, slotted washer head hex screws, and the sensor linkage arm (note whether it uses the short standard arm or the long arm).

4. 4

   Replace the Component

   If the harness tested good during diagnostics, install the new wheel angle sensor body and O-rings.

5. 5

   Reassemble

   Reattach the linkage arm to the sensor and secure the mounting hardware. Reconnect the electrical connector.

6. 6

   Calibration

   Reconnect the battery. You must perform a steering angle sensor calibration using the machine's diagnostic display or service tool. This teaches the steering valve controller the new sensor's center point and left/right end-stop limits.