If you’re asking what a brake relay is, you may have a general idea of what you’re referring to, or you may not. There are two things that “brake relay” may indicate, and it can easily be confusing for anyone if this is a new term.
A brake light switch is sometimes called a brake relay. This is the switch that tells your car’s computer and lights that you’ve pressed the brakes. This sends a signal to turn the lights on and also allows you to shift out of park, or in some cases, turn your car on.
A brake relay valve is a valve that allows large vehicles with air brakes to deliver air to the front and back brakes simultaneously. The valve gets a signal that the brake has been pressed and sends air from a remote supply to activate the rear brakes.
One of these is used every day in every car on the road, and the other is only in vehicles several times larger, but both of them are here for our safety.
What Is A Brake Light Switch
A brake light switch is a small electrical relay attached to the brake pedal. It is typically installed above the brake pedal and (hopefully) activated every time your pedal is pressed. This little switch is extremely important and can create concerning situations if it malfunctions.
When the switch is actuated, the movement completes a circuit that turns on your brake lights and signals to other drivers that you may be slowing down.
This also sends a signal to relevant systems in your car that your brakes are activated. This is important, as most cars will not allow the driver to shift out of park without first receiving a signal that the brake pedal has been pressed.
This can affect certain cars with push buttons by not allowing the car to start if the brake signal is absent – many of them require the brake to be pressed before the button is pushed.
The switch is typically located towards the top of your brake pedal lever. You may have to look around in this area, depending on the car, but this location is often convenient for maintenance purposes.
Possible Failures
You may have a faulty or broken brake light switch if:
- Your brake lights are always on. This can lead to the bulbs burning out much faster – just one more thing you’ll have to worry about. Drivers behind you won’t have a reliable signal when you decide to stop, and the lights will be a constant and unnecessary drain on your battery.
- Your brake lights don’t work at all. In this case, your battery won’t have the drain, but the cars behind you won’t have any idea that you intend to stop. This can obviously lead to an accident.
- As mentioned before, your car won’t shift out of park. This could happen for several reasons, but a bad switch is an easy thing to check.
- Your push button start won’t work, even after you press the brake pedal.
- Any of the aforementioned issues happen, but intermittently. This could indicate a sticky switch or a loose connection. This may turn on the Check Engine or ABS light on your dashboard.
Remember that you can easily have police attention focused on you if they notice a safety hazard like dysfunctional brake lights. It will be much easier and less stressful for you to fix this as soon as you notice the problem.
Brake Light Switch Testing
If you have a 12 volt test light or a multimeter, there’s a good chance that you’ll be able inspect the switch with just a few minutes.
- Find the switch near the top of the brake pedal. Just make sure it’s there, and that it hasn’t broken or fallen off. You may want to find a picture of an identical switch on the internet so you can easily confirm that it is not cracked or broken.
- Ensure that the wires are all securely fastened to the switch. None of them should be loose or disconnected. If they are, make sure that the car is off before you reconnect them. Use the owner’s manual to confirm the correct location for each wire.
- Press the brake pedal to make sure that the alignment of the switch is correct. The top of the brake pedal should press the button on the switch.
- Use your owner’s manual or an online resource to determine which leads on the switch to test with a 12 volt light or a multimeter.
What is a Brake Relay Valve
A brake relay valve is a valve often used in the air brake systems of large vehicles like eighteen-wheelers, buses, and even trains.
As a side note, air is used as an alternative to hydraulic fluid (also called brake fluid) in large vehicles for several reasons:
- Air is an unlimited resource, which eliminates the need to buy large amounts of brake fluid.
- Small leaks won’t prevent the air brakes from working and pollute the environment as a similar leak would with a hydraulic system.
- Air getting into the brake lines is no longer a serious problem. Bleeding and flushing the brake lines is now unnecessary.
- Air not only serves as a fluid for transmission of force, but also stores potential energy as it is compressed, so it can serve to control the force applied; hydraulic fluid is not as compressible as air.Air brake systems include an air tank that stores sufficient energy to stop the vehicle if the compressor fails.
Unfortunately, air doesn’t always travel fast enough when we need it to stop large vehicles. It takes longer for the supply to reach the back brakes than the front. This is called brake lag, and if left unchecked, would extend the stopping distance of these trucks and buses.
This could lead to the front brakes wearing out significantly faster than usual. It could also lead to you being run over when a bus can’t stop quickly enough.
The solution to this problem, the relay valve, receives a signal to open when the driver presses the brake pedal and allows air to be sent to the rear brakes simultaneously.
Do I Have One In My Car
At this point, you can easily guess that, no, you don’t have a brake relay valve in your car. This is actually quite fortunate for you.
Imagine if the average car used air to activate the brakes, rather than hydraulic fluid. In this case, it’s still unlikely that it would need a relay, as the car would be short enough for the air to reach the brakes quickly, but that’s not the issue.
Any moisture that enters a car’s air lines in the winter would freeze, making the brakes useless if the compressor can’t deliver air through a blocked hose.
The compressor needed to supply the air would just be another electrical load that could have been avoided. It would also add a lot of unnecessary weight, which would affect the base fuel efficiency of the car.
Air brakes have a reserve (a usable collection of “standby air”) that is used every time the brakes are applied. The container for this would also add more unnecessary weight to the car, but there’s an even bigger problem.
If the user isn’t careful, they could easily deplete the reserve. Imagine their shock when – surprise! – they have to wait for the compressor to catch up before they can use their brakes again.
In larger vehicles, depleting all of the usable air means that the emergency brakes will automatically activate. So, what sounds like more fun for a minivan full of kids. No brakes or sudden brakes?
Trust the engineers who design these systems. They know what they’re doing.
