Left Tail Light Circuit Open
What does B0040 mean?
The B0040 code means the vehicle's onboard diagnostic system has detected: Left Tail Light Circuit Open. This is a moderate severity code.
Common Symptoms
- Left tail light not illuminating at night
- Tail light warning on dashboard
- Left side of vehicle dark when headlights on
- Rear left license plate area dim
- Failed safety or emissions inspection
Probable Causes (Ranked by Likelihood)
- Burned out left tail light bulb Very High
- Corroded tail light bulb socket High
- Open circuit in tail light wiring Moderate
- Blown tail light fuse Low
Step-by-Step Diagnostic Procedure
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Inspect left tail light bulb for damage
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Check bulb socket contacts for corrosion
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Test voltage at socket with headlights on
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Check tail light fuse in fuse box
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Inspect wiring and connectors to left tail light assembly
Frequently Asked Questions
What is the difference between a tail light and brake light?
The tail light comes on whenever the headlights are on and provides a low-intensity red glow for visibility. The brake light activates only when the brake pedal is pressed and is much brighter.
Can water in the tail light housing cause this?
Yes. Moisture intrusion can corrode bulb sockets and wiring connectors over time, leading to open circuits. Check for cracked lenses or worn gaskets on the tail light housing.
Is the tail light fuse shared with other circuits?
Often yes. The tail light fuse may also power the instrument cluster backlighting and license plate lights. If all of these stop working together, a blown fuse is very likely.