GM BCM FB Repair Troubleshooting Guide

Important: Please do not open or disassemble the module. This guide is meant to rule out common vehicle-side causes first (battery, fuses, power/ground, wiring, and connectors).

• Step 1: Confirm the exact symptom
  • Door locks work randomly/intermittently, BCM no communication, and/or power windows won’t go up or down
  • Note whether the issue is constant, intermittent, or happens after rain/wash/temperature changes
• Step 2: Verify battery voltage and charging health
  • Low voltage can cause BCM dropouts and intermittent body functions
  • If the battery was recently dead/jump-started, fully charge and re-test
• Step 3: Check the basics first (quick wins)
  • Confirm the key fob battery is good (for lock concerns)
  • Confirm the window lock switch is not engaged (for window concerns)
  • Confirm the vehicle is not in a low-voltage / protection mode message state
• Step 4: Check fuses related to BCM/locks/windows
  • Check BCM/body fuses and any power window/door lock fuses
  • If a fuse is blown, replace it once and re-test
  • If it blows again, stop and inspect the circuit for a shorted actuator/motor or damaged wiring
• Step 5: Perform a full vehicle scan
  • Scan all modules, not just the engine
  • Record BCM codes and any network/communication codes
  • Clear codes and see what returns immediately
• Step 6: Confirm BCM communication
  • If the scan tool cannot connect to the BCM:
    • Focus on Step 7 and Step 8 (power/ground and connector checks)
  • If other modules also won’t communicate:
    • Suspect vehicle-side power/ground or network issues first
• Step 7: Verify BCM power and ground
  • Confirm constant battery power feeds and ignition power feeds (key on) to the BCM/fuse box
  • Confirm grounds are solid under load (weak grounds can cause intermittent locks/windows and no-comm)
• Step 8: Inspect connectors for corrosion, water intrusion, or loose terminals
  • Inspect for green corrosion, moisture residue, bent/pushed-out pins, loose terminals, or heat damage
  • Reseat connectors fully and ensure locking tabs are secured
  • If symptoms change when moving the harness, suspect connector fitment or terminal tension
• Step 9: Rule out common “not-the-BCM” causes
  • If only one door/window is affected, inspect that door’s actuator/regulator and door-jamb wiring first
  • If windows fail but locks work, inspect window master switch operation and door harness wiring
  • If locks fail but windows work, inspect lock actuators and door harness wiring
  • If the issue started after audio/remote-start/alarm install, inspect splices and modules tied into door/BCM circuits
• Step 10: Re-test with multiple inputs
  • Door locks: key fob + interior lock switch
  • Windows: driver master switch + individual door switch (if equipped)
  • Repeat multiple cycles to confirm consistency
• Step 11: Re-scan after re-test
  • Check which BCM codes returned after testing
  • Note any codes that return immediately vs. only after operating locks/windows
• If the issue is still present
  • Call or email UpFix for the fastest help, especially if the issue happens immediately after install