Case IH 15321 - AST – AST (Auto Guidance / Steering) / Steering Valve Controller: Steering valve controller failure - LVDT signal A out of range

The LVDT (Linear Variable Differential Transformer) monitors the physical position and movement of the steering valve spool. "Signal A out of range" indicates that the voltage feedback from this sensor has dropped below or exceeded the calibrated acceptable limits. This typically points to an electrical issue such as an open circuit, a short circuit, or a complete failure of the sensor itself.

• MAXXUM T4E
• VESTRUM CVX
• Farmall 40
• Farmall 45
• Farmall 50
• Puma
• Magnum
• Steiger

1. 1

   Inspect the wiring harness and connectors between the AST steering valve controller and the LVDT sensor. Look for corrosion, moisture ingress, or backed-out pins.

2. 2

   Using a multimeter, verify that the LVDT sensor is receiving the correct reference voltage and has a solid ground connection.

3. 3

   Test the 'Signal A' wire for continuity from the sensor connector back to the controller. Check for a short-to-ground or short-to-power.

4. 4

   Ensure the steering valve spool is not physically sticking or jammed, which could force the sensor to read an out-of-bounds position.

1. 1

   Power Down

   Turn off the tractor, remove the key, and disconnect the battery to prevent electrical shorts.

2. 2

   Locate the Valve

   Locate the hydrostatic steering control valve and the attached PVED-CLS actuator/controller.

3. 3

   Harness Repair

   If the diagnostic checks revealed damaged wiring or a corroded connector, repair the harness or splice in a new pigtail connector.

4. 4

   Component Replacement

   If the wiring is intact, the LVDT sensor has failed. Remove and replace the entire steering valve actuator module (on the Danfoss PVED-CLS steering valves used by Case IH, the LVDT sensor is often integrated directly into the actuator head).

5. 5

   Reassembly

   Install the new actuator/sensor, torque mounting bolts to OEM spec, and reconnect the wiring harness.

6. 6

   Calibration

   Reconnect the battery. You must use the tractor's instrument cluster menus or an electronic service tool to clear the fault codes and perform a steering valve calibration. This teaches the AST controller the new LVDT center and end-of-stroke voltage values.