Case IH 518889-03 - BCM – Body Control Module (BCM): Ambient White Illumination Shorted to High Source

The circuit responsible for powering the ambient white illumination (typically interior cab lighting) has short-circuited to battery voltage (B+).

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

1. 1

   Verify voltage drop and ensure power is coming from the correct source (circuit is receiving 12V when it shouldn't be)

2. 2

   Inspect the ambient lighting cable and wiring harness for physical damage, looking for worn or chafed cables exposing wires to a 12V power source

3. 3

   With power disconnected, remove the lighting circuit cable from the BCM and test for continuity between the circuit pins and the tractor's B+ (positive 12 volts). If resistance is extremely low, the short is confirmed in the harness or the light fixture.

1. 1

   Turn the vehicle ignition to the Key OFF position and disconnect the battery to prevent electrical damage.

2. 2

   Locate the Body Control Module (BCM) and disconnect the specific connector for the ambient white illumination driver.

3. 3

   Trace the wiring harness from the BCM to the ambient light fixtures.

   Repair or replace any damaged, pinched, or chafed sections of the wire that are shorting to a positive voltage source.

4. 4

   If the wiring harness tests fine (resistance is normal), inspect the ambient light fixtures themselves for internal shorts.

   Replace the fixture if defective.

5. 5

   Reconnect the repaired harness and the battery.

6. 6

   Turn the vehicle ignition to Key ON, Engine OFF to allow the system to read all Diagnostic Trouble Codes (DTCs).

7. 7

   Enter Diagnostic mode via the tractor's display (e.g., AFS Pro) or an Electronic Service Tool, and clear the inactive DTCs.