B1806 Tail Lamp Output Circuit Malfunction
The B1806 code indicates a fault in the tail lamp output circuit, which is a manufacturer-specific code primarily used by Toyota and its affiliates. This code is triggered when the Body Control Module (BCM) or lighting module detects an anomaly in the circuit powering the rear lights, including tail, brake, and license plate lamps. The system monitors voltage and current in the output circuit; if it detects an open circuit, short to ground, short to battery, or abnormal resistance outside manufacturer specifications, the fault code is set.
1. Commonly Affected Makes
2. Most Common Causes
- Blown fuse in the tail lamp circuit
- Burnt-out tail lamp bulb or damaged filament
- Corroded, shorted, or open connector or wiring
- Faulty Body Control Module (BCM)
- Excessive resistance in the ground circuit
- Damaged output actuator in the lighting module
- Short circuit between wires in the rear lamp harness
3. Symptoms You Will Notice
- Tail lamps, brake lights, or license plate lights inoperative
- Dim or flickering rear lights
- Blown fuse repeatedly
- Warning light on the dashboard
4. Step-by-Step Diagnosis
Check and replace any blown fuses in the tail lamp circuit.
Inspect all rear bulbs for continuity and replace if burnt out.
Visually examine wiring and connectors for corrosion, damage, or loose connections.
Test circuit continuity and resistance from BCM to tail lamps using a multimeter.
Check for shorts to ground or battery voltage in the harness.
If all else is normal, suspect a faulty BCM or lighting module and perform module diagnostics.
5. Frequently Asked Questions
Is it safe to drive?▼
Driving with this code is not recommended because inoperative rear lights reduce visibility and increase the risk of a collision or traffic citation. Have the issue diagnosed promptly.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on the cause. A simple bulb or fuse replacement may cost under $50, while BCM replacement can exceed $500 including labor.