Case IH 520206-30 - VCM – UCM / VCM: Steering valve controller roading switch voltage missing at startup

This fault indicates a communication or electrical failure in the autoguidance/steering system where the controller is not receiving the correct voltage signal from the roading switch (also known as the master switch or field/road mode switch). When this fault is active, the system defaults to a fail-safe mode, locking out the autoguidance system and defaulting to standard hydraulic steering.

• MAGNUM AFS Connect
• Case IH Magnum AFS Connect
• Case IH Steiger / Quadtrac AFS Connect
• Case IH Optum

1. 1

   Ensure the roading switch (located on the right-hand overhead panel or headliner) is not physically stuck between positions

2. 2

   Check the status of the roading switch and steering mode on the Pro 1200 display ISOBUS diagnostic page (if it reads 'On-Road' regardless of physical switch position, the circuit is open or shorted)

3. 3

   Inspect the UCM/VCM controller ground mounting bolts for rust and dirt, which can cause voltage dropouts and false switch codes

4. 4

   Check the wiring harness directly behind the roading switch in the headliner to ensure the connector has not vibrated loose

1. 1

   Power Down

   Turn off the tractor and turn the battery disconnect switch to the OFF position to prevent shorting the CAN bus network.

2. 2

   Clean Controller Grounds

   Locate the UCM/VCM controller mounting bolts. Remove the bolts, wire brush the mounting surfaces and the ring terminals to bare metal, apply dielectric grease, and reinstall securely.

3. 3

   Test the Roading Switch

   Remove the right-hand overhead panel to access the back of the roading switch. Disconnect the switch and use a multimeter to test for continuity across the pins in both the engaged and disengaged positions. If the switch fails to close the circuit or shows high resistance, it must be replaced.

4. 4

   Inspect the Harness

   If the switch tests good, probe the harness connector for 12V reference voltage (with the key ON). If voltage is missing, trace the wiring down the cab pillar to the UCM to locate the break or chafed wire.

5. 5

   Replace Components

   Install the new roading switch or repair the harness terminal as needed.

6. 6

   Clear Codes and Calibrate

   Power the tractor back on. Use the Pro 1200 display or the dealer Electronic Service Tool (EST) to clear the fault history.

7. 7

   Recalibrate

   You must perform the Advanced Steering Valve calibration and Wheel Angle Sensor calibration before the autoguidance system will re-engage.