B1809: Lamp Tail Output Circuit Short To Ground
MediumBodyLighting
What does B1809 mean?
B1809 is a diagnostic trouble code indicating "Lamp Tail Output Circuit Short To Ground". The ECU is detecting a voltage reading that is below the expected range in the lighting circuit. This typically points to a wiring short, a faulty sensor, or a grounding issue.
Symptoms you may notice
- Check engine light (MIL) illuminated on dashboard
- Intermittent warning lights
- Erratic gauge readings
Estimated repair cost
Typical range in Australia (parts + labour)
$100 – $500 AUD
Common causes
- Damaged or corroded wiring harness
- Loose or disconnected electrical connector
- Failed lighting sensor or actuator
- Blown fuse in the related circuit
- Poor ground connection
What should you do?
This code sits in the exterior lighting. Nothing about how the car drives changes, but how easily other road users see you does, and a light out is an on-the-spot fine and an inspection failure. Worth sorting before you next drive at night.
Get a diagnosis for YOUR car
Code B1809 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.