Fiat BCM FB Troubleshooting Guide

Important: Use this guide if you reinstalled your repaired Fiat BCM Fuse Box and the problem is still happening.

• Step 1: Confirm the exact symptom

  • One or both headlights are stuck ON, stuck OFF, or not working

  • Trunk latch will not release or works intermittently

  • Note if the issue started after battery work, fuse work, a collision, or water exposure

• Step 2: Verify battery voltage and charging health

  • Low voltage can cause the BCM to behave erratically (lights acting up, trunk release issues)

  • If the battery was recently dead or jump-started, fully charge it and re-test

• Step 3: Check the basics first

  • Confirm the headlight switch is operating normally (not physically damaged/loose)

  • Confirm the trunk can open mechanically (key/manual release, if equipped) to rule out a jammed latch

• Step 4: Check related fuses first

  • Check fuses for BCM/body functions, headlights/lighting circuits, and trunk/liftgate release

  • If a fuse is blown, replace it once and re-test

  • If it blows again, stop—inspect wiring and the load for a short before suspecting the BCM

• Step 5: Perform a full vehicle scan

  • Scan all modules, not only the engine

  • Record BCM codes and any communication/network codes

  • Clear codes and see what returns immediately

• Step 6: Confirm BCM communication

  • Verify your scan tool can connect to the BCM

  • If the BCM does not communicate, go straight to Step 7 and Step 8

• Step 7: Verify BCM power and ground

  • Confirm constant battery power feeds and ignition feeds (key on) to the BCM/fuse box

  • Confirm grounds are solid under load (weak grounds can cause lights stuck on/off and trunk release issues)

• Step 8: Inspect and reseat BCM/fuse box connectors

  • Inspect for corrosion/green pins, moisture, bent/pushed-out pins, loose terminals, or heat damage

  • Reseat connectors fully and confirm all latches lock

  • If the symptom changes when moving the harness, suspect terminal tension/connector fitment

• Step 9: Headlight-specific checks (stuck ON or not working)

  • Inspect headlamp bulbs and headlamp connectors for heat damage or corrosion

  • Inspect front harness areas for rub-through/shorts (especially near headlights and radiator support)

  • If one headlight is affected, suspect bulb/connector/wiring at that side first

  • If both headlights act up together, focus on BCM power/ground and connector integrity

• Step 10: Trunk latch-specific checks (no release)

  • Verify the latch isn’t mechanically jammed and the striker alignment is not binding

  • Inspect trunk harness near hinge areas for broken wires (common)

  • If the latch works intermittently, focus on hinge-area wiring and connector seating first

• Step 11: Check for recent work that could have triggered it

  • If the issue started after a battery replacement, fuse work, stereo work, or body repair

  • Re-check anything that was unplugged, grounded, or spliced during that work

• Step 12: Re-test and re-scan

  • Re-test headlights and trunk release multiple times

  • Re-scan and note any codes that return immediately vs. only after operating the functions

• If the issue is still present

  • Call or email UpFix for the fastest help, especially if the issue happens immediately after install