B1807 — Lamp Tail Output Circuit Open #

Note: The description of this Diagnostic Trouble Code (DTC) may vary depending on the vehicle manufacturer.

• B1807: Tail Lamp Output Circuit Open (Ford, Lincoln, Mercury)
• B1807: Rear Lamp Output Open (Toyota, Lexus)
• B1807: Taillight Circuit Malfunction (Nissan, Infiniti)

Summary of Code B1807 #

The B1807 code is an OBD-II/Body Control Module (BCM) diagnostic trouble code that indicates an open circuit has been detected in the tail lamp output circuit. In simple terms, this means the system has noticed a break or interruption in the wiring or connection responsible for sending power from the control module to the rear tail lamps. This code is most commonly triggered when the vehicle’s onboard computer, such as the Body Control Module (BCM), does not detect the expected electrical continuity in the circuit. Because taillights are crucial for visibility and safety, especially at night or in poor weather, this code should not be ignored. The exact naming or implications of B1807 might change between OEMs (Original Equipment Manufacturers), but the root cause remains a disruption in the tail lamp circuit integrity.

Common Symptoms for Code B1807 #

When B1807 is set, you’ll usually notice that your vehicle’s tail lamps are not functioning properly. This can range from a single taillight being out to both rear lights being nonfunctional. Sometimes, the issue may be intermittent, making it tricky to spot until someone points it out or you inspect the lights yourself. Modern vehicles might display a warning message or indicator light on the dashboard. Here are the most common symptoms:

• One or both tail lamps not illuminating
• Rear lighting malfunction warning on dashboard
• Intermittent tail lamp operation
• No voltage present at the tail lamp socket
• Other rear lights (e.g., brake or turn signals) working normally

Probable Causes for Code B1807 #

The most likely root causes for a B1807 Lamp Tail Output Circuit Open code are related to wiring, connectors, or the BCM itself. Since “open circuit” means there’s a break somewhere between the power source and the lamp, you’ll want to focus on anything that could interrupt that flow. Here’s the list of probable causes, in order of likelihood:

1. Damaged or corroded tail lamp wiring harness
2. Loose, disconnected, or corroded tail lamp connector
3. Burnt-out tail lamp bulb (less common, as most systems detect this differently)
4. Faulty Body Control Module (BCM) or rear electronic module
5. Poor ground connection at the tail lamp assembly
6. Aftermarket wiring modifications causing circuit interruption

Step-by-Step Diagnosis for Code B1807 #

Diagnosing a B1807 code involves systematically checking the tail lamp circuit for breaks, corrosion, or poor connections. Using a digital multimeter, test light, and sometimes a scan tool with BCM access, you can narrow down the fault. Here’s a proven step-by-step diagnostic approach:

• Verify the complaint: Check if the tail lamps are actually not working as described.
• Inspect bulbs: Ensure the tail lamp bulbs are the correct type and not burnt out.
• Check fuses: Locate and check the relevant fuse(s) for the tail lamp circuit in the fuse box.
• Visual inspection: Examine wiring harnesses and connectors for damage, corrosion, or loose pins, especially near the tail lamp and BCM.
• Test for voltage: With the lights switched on, use a multimeter to check for 12V at the tail lamp socket.
• Check ground: Test the ground circuit at the lamp socket to ensure it is intact.
• Backprobe BCM output: If no voltage at the lamp, check for output directly at the BCM (consult wiring diagram for location).
• Scan for additional codes: Use a scan tool to check for related DTCs that may indicate a module or communication issue.
• Isolate circuit section: If necessary, disconnect wiring at intermediate connectors to isolate the fault to a specific section.
• Test after repairs: After any repair, clear the code and retest the circuit and lamp operation.

Possible Repairs for Code B1807 #

Once you’ve identified the fault, repairing a B1807 code usually involves restoring circuit integrity or replacing a faulty component. Use only OEM (Original Equipment Manufacturer) parts for best results, especially for connectors and modules. Typical repairs include:

• Repair or replace damaged tail lamp wiring harness
• Clean or replace corroded connectors at the tail lamp or BCM
• Replace the tail lamp bulb (if faulty)
• Repair or improve the ground connection at the tail lamp assembly
• Replace faulty Body Control Module (BCM) or rear electronic module (after confirming diagnosis)
• Restore any improperly modified or aftermarket wiring

Is It Safe to Drive with Code B1807? #

Driving with a B1807 code is limited and not recommended for night or low-visibility conditions. Since the tail lamps may not work, your vehicle could be nearly invisible from the rear, posing a serious safety risk to you and others. If you must drive, do so only during daylight hours and have the issue repaired as soon as possible. In many regions, driving without working tail lamps is also illegal and could result in a citation.

Vehicles Most Commonly Affected by Code B1807 #

While the B1807 code can appear on many vehicles equipped with OBD-II/EOBD and a Body Control Module, it’s most frequently reported on certain makes and models. Here are some that often use this code:

• Ford F-Series (F-150, F-250, etc.)
• Ford Explorer, Ford Taurus, Ford Edge
• Lincoln MKX, Lincoln Navigator
• Toyota Camry, Toyota Highlander
• Lexus RX, Lexus ES
• Nissan Altima, Nissan Murano
• Infiniti FX and QX series

Common Mistakes & Best Practices for Code B1807 #

When troubleshooting B1807, even experienced techs can make simple errors. Avoiding these will save time and prevent repeat failures. Here’s what you should watch for:

• Replacing bulbs without checking wiring or connectors first
• Overlooking corrosion inside connectors, especially in wet climates
• Failing to check for blown fuses or shared circuits
• Ignoring possible BCM faults if wiring and bulbs check out
• Not verifying proper ground at the tail lamp assembly
• Using incorrect replacement bulbs or connectors
• Not clearing the code after repairs

Express FAQ for Code B1807 #

Q: Can a blown bulb alone trigger the B1807 code?
A: It’s possible, but most modern vehicles will set a different code for a failed bulb. B1807 typically points to a wiring or connector problem, not just a burnt bulb.

Q: Do I need a scan tool to fix B1807?
A: While a scan tool helps confirm and clear the code, most electrical checks (voltage, ground, continuity) can be done with a digital multimeter and basic tools. For BCM issues, a scan tool with body module access is recommended.