Case IH 519109-07 - UCM – UCM: Trailer brake test switch stuck

The control module is detecting that the trailer brake test rocker switch is continuously engaged. This usually means the switch is physically jammed in the depressed position, the internal contacts have welded/stuck together, or there is a short in the wiring harness mimicking a pressed switch.

• MAGNUM AFS Connect
• Case IH Magnum AFS Connect series
• Case IH Puma series (200, 215, 230, etc.)

1. 1

   Locate the trailer brake test switch (on the C-pillar or right-hand armrest) and physically inspect it for dirt, debris, or spilled liquids causing it to jam.

2. 2

   Firmly press and release the switch several times to see if the internal spring mechanism frees up.

3. 3

   Perform an electrical continuity test on the switch: disconnect the wiring harness and test for continuity. If it shows a closed circuit without being pressed, the internal contacts have failed.

4. 4

   If the switch tests fine, check the wiring harness leading back to the UCM for a short to power or ground.

1. 1

   Power Down

   Turn off the tractor ignition and engage the electronic battery isolator to prevent electrical spikes.

2. 2

   Remove the Switch

   Using a plastic non-marring trim tool, carefully pry the edges of the faulty trailer brake test rocker switch to release its retaining clips from the C-pillar or armrest console panel.

3. 3

   Disconnect

   Pull the switch forward and unplug the electrical connector from the rear of the switch.

4. 4

   Install New Part

   Plug the tractor's wiring harness connector into the new OEM rocker switch.

5. 5

   Reassemble

   Push the new switch firmly back into the console cutout until the plastic retaining clips snap into place.

6. 6

   Clear Codes

   Turn the battery isolator back on, cycle the ignition key, and use the AFS Pro display (or a diagnostic scan tool) to clear the inactive 519109-07 fault code from the UCM.

7. 7

   Verify Operation

   Perform a trailer brake test to ensure the system engages properly and the fault code does not return.