Case IH 520579-06 - BCM – BCM: Short circuit to ground on the rear left turn signal circuit

The Body Control Module (BCM) has detected a short circuit to ground on the rear left turn signal circuit. The voltage intended to power the turn signal bulb or LED is finding a premature path directly to the chassis ground, causing the BCM to disable power to this specific circuit and the rear left turn signal to stop working.

• MAGNUM AFS Connect
• Magnum
• Steiger
• Puma
• Optum
• Maxxum

1. 1

   Visually inspect the rear left turn signal housing for physical damage, cracked lenses, or water ingress, which is a leading cause of internal shorts.

2. 2

   Disconnect the electrical connector directly at the rear left turn signal assembly, turn the ignition on, and check if the code changes from 'Short to Ground' (FMI 06) to 'Open Circuit' (FMI 05) to isolate the short to the light assembly.

3. 3

   Trace the wiring harness from the rear left fender back toward the BCM, looking for areas where the harness may be rubbing against the frame, pinched by cab mounts, or melted by exhaust components.

4. 4

   With the battery disconnected and the BCM and light assembly unplugged, use a digital multimeter to test for continuity between the turn signal power wire and a known good chassis ground.

1. 1

   Power Down

   Turn off the ignition and disconnect the negative battery terminal to prevent accidental shorts during repair.

2. 2

   Address the Short

   If the light assembly is internally shorted: Unbolt the damaged rear left turn signal assembly from the fender/cab bracket. Install the replacement assembly and plug in the weather-sealed connector. If the wiring harness is shorted: Locate the chafed or pinched section of the wire. Cut out the damaged section of copper. Strip the ends and splice in a new section of automotive-grade wire using weather-sealed, heat-shrink butt connectors. Wrap the repaired section in protective split-loom tubing and secure it away from sharp edges with zip ties.

3. 3

   Reassemble and Power Up

   Reconnect the negative battery terminal.

4. 4

   Verify Operation

   Turn the ignition key to the ON position and activate the left turn signal. Verify that the light flashes correctly and that the dash indicator works.

5. 5

   Clear Codes

   Use the tractor's AFS Pro monitor or a dealer diagnostic tool to clear the inactive 520579-06 fault code from the BCM's memory.