Case IH 2380-05 - BCM – Body Control Module (BCM): Trailer marker lamps - open circuit

An "open circuit" fault for the trailer marker lamps means the control module is detecting a current draw that is below normal or zero on that specific circuit. This typically indicates a broken wire, a disconnected or corroded trailer plug, a burnt-out bulb, or a blown fuse. Additionally, modern CAN bus systems expect a steady, specific current draw; if a trailer has been retrofitted with non-CAN-compatible LED lamps, the LEDs will draw too little current, causing the system to falsely flag an "open circuit" or "bulb failure" warning.

• MAGNUM AFS Connect
• Case IH Magnum
• Optum AFS Series
• Steiger

1. 1

   Verify Connections: Ensure the trailer plug is fully seated and make proper trailer connections.

2. 2

   Voltage Test: Turn on the headlights/marker switch. Verify that the marker/tail light pins on the tractor's rear receptacle have battery voltage present.

3. 3

   Fuse/Relay Check: Check the Power Distribution Module (PDM) for a blown trailer marker lamps fuse or a faulty relay.

4. 4

   Load Check (LEDs): Check if the trailer is using aftermarket LED lamps. If they are not CAN-compatible, they will not draw enough current to register on the BCM.

1. 1

   Inspect the Receptacle

   Check the tractor-side and trailer-side connectors for corrosion, pushed-out pins, or broken wires. Clean the contacts or replace the receptacle if damaged.

2. 2

   Check the Bulbs

   Inspect the trailer marker lamps. Replace any burnt-out halogen bulbs.

3. 3

   Address LED Compatibility

   If the trailer uses LED lights and the wiring is intact, the open circuit code is likely due to low current draw. You must either install CAN-compatible LED lamps (which include built-in resistor packs) or wire in external load resistors to mimic the current draw of a halogen bulb to satisfy the BCM.

4. 4

   Repair Wiring

   If voltage is not reaching the back of the tractor, trace the marker lamp circuit forward to the BCM/PDM, repairing any broken wires or replacing blown fuses along the circuit.

5. 5

   Clear Codes

   Cycle the ignition and re-test the lighting to ensure the BCM registers the correct current draw and clears the active fault.