OBD Code B1807: Lamp Tail Output Circuit Open

Q: What does OBD code B1807 mean?

Lamp Tail Output Circuit Open. The tail lamp circuit has an open connection, meaning electricity cannot flow to power the rear lights. Think of it like a broken wire in a string of Christmas lights—the circuit is interrupted and the lights won't turn on.

Q: How do I fix OBD fault code B1807?

Replace burned-out bulbs in both tail lamp assemblies.. Inspect and reseat all connectors at the tail lamp assemblies and body harness for corrosion or looseness.. Replace the entire tail lamp housing or the tail lamp relay module if wiring and bulbs are intact.

💬

What This Actually Means

In plain language — no jargon

The tail lamp circuit has an open connection, meaning electricity cannot flow to power the rear lights. Think of it like a broken wire in a string of Christmas lights—the circuit is interrupted and the lights won't turn on.

⚡

Symptoms You May Notice

3 known symptoms for this code

Tail lamps do not illuminate when headlights or running lights are activated

Dashboard warning light or message indicating tail lamp malfunction

Reduced visibility to following vehicles at night

🔬

How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the tail lamp output circuit by measuring current flow and voltage at the lamp control module. When the circuit is commanded on, it expects to detect a specific voltage drop and current draw; an open circuit prevents current flow entirely, triggering a fault.

Voltage & Parameter Thresholds

Parameter	Normal Range	Fault Condition
Tail Lamp Current Draw	1.5–3.0 A per circuit	< 0.1 A (open circuit detected)
Circuit Voltage	12–13.5 V with load	No voltage drop or excessive resistance

🔧

Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

Tail lamp bulb(s)

Replace burned-out bulbs in both tail lamp assemblies.

2

Wiring harness and connectors

Inspect and reseat all connectors at the tail lamp assemblies and body harness for corrosion or looseness.

3

Tail lamp assembly or relay

Replace the entire tail lamp housing or the tail lamp relay module if wiring and bulbs are intact.

⚠️

When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1807 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.

🔄

How to Clear Code B1807

What happens after you fix the fault

Once the fault is repaired, B1807 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When

Fault has been diagnosed and repaired
You want to confirm the repair worked
Code appeared after a sensor was cleaned

⚠️ Do Not Clear When

Preparing for an emissions/PUC test
Root cause is still undiagnosed
Check engine light is flashing

Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.