Case IH 520586-03 - BCM – BCM: Trailer left turn indicator - short circuit to B+

The controller has detected that an electrical path exists between the left turn signal circuit and a battery power source when it is not intended to exist. The circuit is receiving constant or unwanted high voltage.

• MAGNUM AFS Connect
• Magnum AFS Connect 180
• Magnum AFS Connect 200
• Magnum AFS Connect 220
• Magnum AFS Connect 240
• Magnum AFS Connect 250
• Magnum AFS Connect 280
• Magnum AFS Connect 310
• Magnum AFS Connect 340
• Magnum AFS Connect 380
• Magnum AFS Connect 400
• Steiger AFS Connect

1. 1

   Isolate the trailer by disconnecting it from the tractor's rear receptacle to see if the fault code goes inactive (indicating the short is in the trailer wiring).

2. 2

   Inspect the tractor's rear trailer receptacle for dirt, water ingress, corrosion, or bent pins that could bridge the left turn signal pin to a constant 12V auxiliary power pin.

3. 3

   With the trailer disconnected and the turn signal switched OFF, use a multimeter to check for voltage at the left turn pin on the tractor's receptacle (presence of 12V indicates a short to power in the tractor's harness).

4. 4

   Visually inspect the wiring harness running from the rear receptacle to the BCM for signs of chafing, melted insulation, or pinch points.

1. 1

   Park the machine safely, turn off the ignition, and disconnect the trailer plug. Clear the fault codes and retest.

2. 2

   If the code remains active on the tractor, disconnect the negative battery cable to prevent further electrical damage.

3. 3

   Disassemble the rear trailer lighting receptacle. Clean out any corrosion. If the terminals are melted together or internally shorted, cut back the wires and install a new receptacle.

4. 4

   If the receptacle is in good condition, trace the wiring harness from the rear of the tractor up to the BCM.

5. 5

   Disconnect the harness at the BCM and test for continuity between the left turn signal wire and any constant battery power wires.

6. 6

   Locate the shorted section of the wiring harness. Repair the damaged wires by splicing in new wire and sealing the repair with heat-shrink tubing.

7. 7

   If the wiring harness tests perfectly (no short to power in the wires) but the BCM continues to output 12V on that pin constantly, the BCM has suffered an internal hardware failure.

8. 8

   Replace the BCM and have a dealer flash the correct software for the tractor's specific configuration.

9. 9

   Reconnect the battery, turn the key to the ON position, and verify the left turn signal operates normally without throwing the code.