B1806 — Lamp Tail Output Circuit Failure #

Note: The description of code B1806 may vary depending on the vehicle manufacturer (OEM). Always refer to your vehicle’s service manual for the most accurate information.

• B1806: Tail Lamp Output Circuit Failure (Ford, Lincoln, Mercury)
• B1806: Rear Lamp Output Circuit Malfunction (Toyota, Lexus)
• B1806: Taillight Output Open/Short (Mazda)

Overview of code B1806 #

The B1806 trouble code indicates a problem in the electrical circuit that controls the rear tail lamp output on your vehicle. When this code is set, it means the Body Control Module (BCM)—the computer responsible for managing body-related electrical systems—has detected a malfunction such as an open circuit, short to ground, or short to voltage in the wiring between the BCM and the tail lamps. In simple terms, the system can’t properly turn on or monitor the rear tail lights, which are crucial for nighttime driving and safety. This code can trigger a warning light on your dash, and may affect your vehicle’s exterior lighting functions. Detecting and fixing this code quickly is important, as a malfunctioning tail lamp can reduce your visibility to other drivers.

Common symptoms for B1806 #

When your vehicle registers code B1806, you may notice several signs indicating trouble with your tail lamp circuit. These symptoms can range from subtle to obvious, and may vary depending on the specific fault or vehicle model. Typically, drivers or technicians will observe:

• Tail lamps not working or intermittently functioning
• Warning light or message on the dashboard
• Other exterior lights (such as brake or parking lights) possibly affected
• Bulb out indicator illuminated
• Electrical burning smell (in rare cases of wiring short)

Probable causes for B1806 #

The most common causes behind the B1806 code relate to issues within the wiring or components of the tail lamp circuit. Some causes are far more frequent than others—here’s what technicians usually find, listed in order of likelihood:

1. Burned-out tail lamp bulb
2. Damaged or corroded bulb socket
3. Broken, frayed, or corroded wiring between BCM and tail lamp
4. Bad ground connection for the rear lighting circuit
5. Faulty tail lamp relay (if equipped)
6. Defective Body Control Module (BCM) (rare)

Step-by-step diagnostic for B1806 #

Diagnosing the B1806 code requires a systematic approach to rule out simple issues before moving on to more complex possibilities. Here’s how a professional technician would typically proceed:

• Check for additional codes: Scan for related lighting or BCM trouble codes.
• Visually inspect all tail lamps: Look for burned-out bulbs or obvious damage.
• Test bulb sockets: Check for corrosion, bent contacts, or looseness.
• Inspect wiring and connectors: Trace wiring from the tail lamps back to the BCM, looking for cuts, frays, or corrosion.
• Test ground connections: Ensure the tail lamp circuit has a clean, secure ground.
• Check relay operation (if applicable): Swap with a similar relay to rule out failure.
• Test BCM outputs: Using a wiring diagram and multimeter, confirm the BCM is sending voltage when the lights should be on.
• Clear the code and retest: After repairs, clear the code and verify proper operation.

Possible repairs for B1806 #

Once the root cause is found, repairs should directly address the specific fault. Here’s a list of common fixes, matched to the probable causes above:

• Replace the burned-out tail lamp bulb
• Clean or replace corroded bulb sockets
• Repair or replace damaged wiring or connectors
• Restore or clean ground connections (sand, tighten, or reconnect as necessary)
• Replace faulty tail lamp relay (if used)
• Replace the Body Control Module (BCM) only if all other options are exhausted and diagnosis confirms failure

Is it safe to drive with code B1806? #

Limited — While your vehicle may technically still operate with code B1806 present, it is not recommended to drive at night or in low-visibility conditions until the issue is fixed. Tail lamps are essential for letting other drivers see your vehicle from behind. Driving without functioning tail lamps is unsafe and may be illegal in many regions. Address this code as soon as possible to avoid potential accidents or fines.

Vehicles most commonly affected by B1806 #

Code B1806 is most frequently reported on vehicles from manufacturers that use advanced BCM-controlled lighting circuits. Based on field experience and technical bulletins, these models are particularly prone to B1806:

• Ford F-Series (F-150, F-250, F-350, various years)
• Ford Explorer, Ford Escape
• Lincoln Navigator
• Toyota Camry, Corolla (select years)
• Lexus RX, ES
• Mazda 3, Mazda 6

Common mistakes & best practices for B1806 #

It’s easy to overlook simple solutions or misinterpret the code, leading to unnecessary part replacements. To avoid common pitfalls:

• Don’t replace the BCM without thorough testing—rarely the root cause.
• Always check bulbs and sockets first, even if they “look” fine.
• Inspect wiring closely, especially at points where it flexes or is exposed to moisture.
• Never ignore ground connections—a loose or corroded ground is a frequent culprit.
• Use the correct replacement bulbs and parts as specified by the OEM.

Quick FAQ for code B1806 #

Curious about B1806? Here are fast answers to common questions:

• Q: Will B1806 turn on my “Check Engine” light?
  A: Not typically—this code usually triggers a specific lighting or body system warning, not the generic Check Engine light.
• Q: Can a bad tail lamp bulb alone cause B1806?
  A: Yes, a simple burned-out bulb is the most common cause. Always check bulbs first before exploring complex repairs.
• Q: Does B1806 mean my car is unsafe to drive?
  A: It’s unsafe at night or in poor visibility because other drivers may not see your vehicle. Fix the issue promptly.