Why is the BYD taillight constantly on?

[VanJoy]

Here are the reasons why the BYD taillight may be constantly on: 1. Lack of brake fluid: It is an indispensable part of the car's braking system. When the driver steps on the brake pedal, the force applied to the pedal is transmitted by the piston of the brake master cylinder through the brake fluid to the brake cylinders located at each wheel, causing the brake pads to contact the wheels and stop the vehicle. Simply add brake fluid to resolve this issue. 2. Taillight bulb damage: The brake fluid reservoir has upper and lower lines. When the brake fluid level drops below the lower line, the sensor next to the reservoir detects this and reflects it through the brake light on the dashboard. If the brake fluid decreases rapidly, it indicates a leak in the braking system. Replacing the bulb can solve this problem.

[VonWilliam]

My car had a similar issue before. If the brake lights stay on constantly, it's usually because the brake pedal switch is stuck or faulty. That component is located right behind the brake pedal - you'll need to crawl under and check if the spring isn't returning properly. Wiring shorts are also quite common, especially near the trunk hinge area where wires often get frayed, causing constant illumination. Another possibility is a glitch in the control module, or accidentally changing vehicle settings that extended the 'follow-me-home' light duration too long. This situation drains the battery heavily - you might not be able to start the car next morning. So don't delay, get it checked at a repair shop immediately. Their diagnostic tool can pinpoint the problem quickly, whereas DIY attempts might create additional issues.

[GrantLee]

I've seen this situation many times, and the main root cause is a faulty brake light switch. The internal contacts of the switch may be stuck or improperly adjusted, causing continuous signal transmission. Wiring issues cannot be ruled out either—check if the rear taillight connector is loose, water-damaged, or corroded, or if the wiring harness has been repeatedly crushed by the trunk. While the probability of a body control module failure is low, it does happen and requires a specialized computer to read the fault codes for confirmation. Also, a heads-up: if both the high-mounted brake light and the side lights are constantly on, it's likely a circuit issue. If only one side is lit, it could be a short circuit in the bulb socket. Address this promptly, otherwise the risk of being rear-ended skyrockets. Driving at night with malfunctioning taillights is practically suicidal.