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Brake lights won’t turn off

Brake lights won’t turn off — how to diagnose and fix

If you run into a situation where your brake lights won’t turn off, there are really only three possibilities:
• The brake light switch has failed or is out of adjustment
• The switch plunger is no longer contacting the brake pedal switch stopper or cushion.
• There’s a problem with the body control module or relay

How does the brake pedal switch work?

Depending on the vehicle, the brake pedal switch is either stationary, affixed to a steel member under the dash, or it’s attached to the brake pedal assembly. It’s a plunger style switch that pops out and turns on the brake lights when you press the brake pedal. Since carmakers want the brake lights to turn on the instant you apply the brakes, proper adjustment is critical. In fact, if you’ve recently replaced the brake pedal switch and your brake lights don’t come on, chances are it’s maladjusted. More on that later.

Step 1: Check the brake pedal cushion to diagnose a Brake lights won’t turn off condition

Most carmakers designed the brake light switch assembly so the plunger contacts a rubber pad rather than hitting the steel brake pedal bracket. The rubber pad, also referred to as a brake pedal switch cushion, snaps into a hole on the pedal bracket or supporting member. They can wear out or fall out of place. Once that happens, the plunger extends into the hole where the pad usually sits, causing the brake lights to stay on all the time.

So your first step is the look under the dash and locate the stop light switch at the upper end of the brake pedal. Locate the brake switch plunger and check for the presence of the rubber pad. If it’s missing, you have two choices; purchase a generic replacement at an auto parts store or a genuine replacement form the dealer. If you purchase a generic replacement, you’ll probably have to modify the retaining button so it fits into the hole on your bracket. Buying from the dealer is always a better choice; they’re simply not that expensive (around $10).

brake lights won't turn off

If the pad is in place and in good condition, the pad isn’t the problem and the switch is most likely out of adjustment or worn out.

Step 2: Check switch adjustment to fix a Brake lights won’t turn off condition

The body of the brake light switch has threads and the switch is adjusted by loosening the two retaining nuts and moving in or out of the bracket or by loosening a clamp or rotating the switch and then moving it in or out from the stopper bracket. The shop manual for your vehicle will show you how to adjust the switch and how much clearance to maintain between the brake light switch plunger and the pad.

nissan stop light switch adjustment

EXAMPLE: Stop light switch adjustment procedure for 2010 Nissan Altima

1.      Loosen the stop light switch by turning it counterclockwise by 45°.
2.      With the pedal pulled up and held by hand, press the stop light switch in until the threaded end contacts the stopper.
3.      With the threaded end of the stop light switch contacting the bracket, rotate the switch clockwise by 45° to lock the switch in place

Step 3: Check switch continuity to fix a Brake lights won’t turn off condition

If the brake pedal stopper cushion is in good condition and in place and the switch is properly adjusted, but the brake lights stay on all the time, chances are the brake light switch has failed. To diagnose, disconnect the electrical connector to the brake light switch. Some brake light switches have only two terminals, while others have more. If your switch has more than two terminals refer to a shop manual to locates the brake light terminals. When the brake pedal is in the full up position, you should have no continuity on the brake light terminals. If you do, replace the brake light switch.

Step 4: Check the body control module and relays

In older vehicles the brake pedal switch actually switches power to the brake lights. But in late model vehicles, the brake pedal switch is only an input to the body control module (BCM). In some vehicles, the BCM completes the circuit to the brake lights, while in other vehicles, the BCM provides the ground circuit for the brake light relay.

If you’ve adjusted the brake light switch properly and tested with your meter to confirm it’s “OFF’, then the problem is in the BCM or the brake light relay. Get a shop manual with wiring diagrams and troubleshoot those components.

©, 2021 Rick Muscoplat

Posted on by Rick Muscoplat

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