Case IH 518394-06 - UCM – UCM: Trailer brake pedal control solenoid current high

The control module has detected that the electrical current flowing through the trailer brake pedal control solenoid circuit exceeds the maximum expected threshold, indicating a short to ground in the wiring harness or an internally shorted solenoid coil.

• MAGNUM AFS Connect
• Magnum 400 AFS Connect

1. 1

   Visually inspect the wiring harness running from the UCM to the trailer brake control valve assembly for chafed wire insulation, pinched wires against the tractor chassis, or melted conduits.

2. 2

   Perform a coil resistance test by disconnecting the electrical connector at the trailer brake pedal control solenoid and measuring resistance across the pins. A reading of 0 ohms or significantly below OEM spec indicates an internally shorted coil.

3. 3

   Perform a harness short test with the solenoid disconnected and the tractor key OFF. Check for continuity between the solenoid signal wire and the tractor chassis ground; continuity indicates a short to ground.

4. 4

   Inspect the pins at both the solenoid and the UCM for corrosion, water intrusion, or bent pins that could bridge the circuit.

1. 1

   Park the tractor on a level surface, apply the parking brake, turn off the engine, and disconnect the battery ground cable to prevent electrical spikes.

2. 2

   Locate the trailer brake control valve assembly.

   Typically mounted near the rear axle or hydraulic valve stack, depending on whether the tractor is equipped with pneumatic or hydraulic trailer brakes.

3. 3

   Disconnect the wiring harness connector from the faulty trailer brake pedal control solenoid.

4. 4

   Remove the retaining nut or screw that secures the solenoid coil to the valve stem cartridge.

5. 5

   Slide the shorted solenoid coil off the valve stem.

   Note: If the hydraulic/pneumatic cartridge itself is leaking or damaged, the entire valve assembly may need to be replaced, requiring system depressurization first.

6. 6

   Slide the new OEM solenoid coil onto the stem and secure it with the retaining nut/screw.

7. 7

   Reconnect the electrical harness connector, ensuring the weather seal is intact.

8. 8

   Reconnect the battery, start the tractor, and actuate the brake pedal to verify the trailer brake engages and the 518394-06 fault code clears.