Diagnosing B109B Code: Ford License Plate Light Circuit Fault Explained

Diagnosing B109B Code: Ford License Plate Light Circuit Fault Explained

If you’re a Ford vehicle owner or a car enthusiast, encountering an OBD-II Diagnostic Trouble Code (DTC) can be a bit daunting. One such code is B109B, which specifically relates to issues with the license plate light. This blog post will delve into what the B109B code means, its implications for vehicle performance and emissions, and how to diagnose and fix this issue. We’ll also list the top 20 Ford vehicles commonly affected by this code and provide a comprehensive FAQ section to address common concerns.

What is the B109B Code?

The B109B trouble code indicates a fault with the license plate light circuit. This code is set by the Body Control Module (BCM) when the license plate light is not functioning to factory specifications. This could be due to a faulty light, an open or shorted harness, or a problem with the BCM itself.

Top 20 Ford Vehicles Commonly Affected by the B109B Code

  1. Ford F-150
  2. Ford Escape
  3. Ford Explorer
  4. Ford Fusion
  5. Ford Edge
  6. Ford Mustang
  7. Ford Focus
  8. Ford Ranger
  9. Ford Expedition
  10. Ford Transit Connect
  11. Ford Super Duty F-250
  12. Ford Super Duty F-350
  13. Ford Taurus
  14. Ford Flex
  15. Ford C-Max
  16. Ford EcoSport
  17. Ford Fiesta
  18. Ford Bronco
  19. Ford Maverick
  20. Ford Transit

Implications for Vehicle Performance and Emissions

While the B109B code primarily affects the license plate light, it can have broader implications:

  • Visibility and Safety: A malfunctioning license plate light can reduce visibility, making it difficult for other drivers to see your vehicle’s registration plate at night.
  • Legal Issues: Driving with a non-functional license plate light can result in traffic violations and fines.
  • Electrical System: Persistent issues with the light circuit can indicate broader electrical problems that might affect other vehicle systems.

Diagnosing the B109B Code

Diagnosing the B109B code involves a few steps:

  1. Visual Inspection: Check the license plate light for any visible damage or burnt-out bulbs.
  2. Wiring Inspection: Inspect the wiring harness for any signs of wear, open circuits, or shorts.
  3. Multimeter Testing: Use a multimeter to check for continuity and voltage in the light circuit.
  4. BCM Check: If the light and wiring are intact, the issue might lie with the BCM, which may require professional diagnostics.

Fixing the B109B Code

Here are some steps to fix the B109B code:

  • Replace the Bulb: If the bulb is burnt out, replace it with a new one.
  • Repair Wiring: Fix any open or shorted wires in the harness.
  • Clean Connections: Ensure all electrical connections are clean and secure.
  • BCM Reset or Replacement: If the BCM is faulty, it may need to be reset or replaced by a professional.

Key Symptoms and Solutions


  • License plate light not illuminating
  • Intermittent light functionality
  • Warning light on the dashboard


  • Replace faulty bulbs
  • Repair or replace damaged wiring
  • Clean and secure electrical connections
  • Reset or replace the BCM

FAQ Section

Q: Is it safe to drive with the B109B code? A: While it may not immediately affect driving performance, it’s unsafe and illegal to drive without a functioning license plate light, especially at night.

Q: What are the potential repair costs? A: Repair costs can vary. Replacing a bulb is inexpensive, but wiring repairs or BCM replacement can be more costly, ranging from $50 to several hundred dollars depending on the complexity.

Q: How can I prevent this issue in the future? A: Regularly inspect your vehicle’s lights and wiring. Keep electrical connections clean and secure, and address any electrical issues promptly.


Addressing the B109B trouble code promptly is crucial for maintaining your Ford vehicle’s safety, legality, and overall performance. Regular maintenance and timely repairs can help prevent such issues, ensuring your vehicle remains efficient and compliant with emission standards. If you encounter this code, follow the diagnostic steps outlined above or consult a professional mechanic to resolve the issue effectively.

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