Most drivers know that the parking brake is there to keep a parked vehicle from moving. But what happens if you are driving and the service brakes suddenly stop working?
With a conventional mechanical parking brake, the driver operated the brake directly through a hand lever or foot pedal. The mechanism was mechanically connected to the parking brakes, usually on the rear wheels. Depending on the vehicle and the driver's technique, the brake could be applied progressively and released again if necessary.
That did not make a conventional parking brake a substitute for the service brakes. Applying the rear brakes too aggressively could still cause the rear wheels to lose traction and the vehicle to become unstable. The difference was that the driver had direct mechanical control over how the brake was applied.
An electronic parking brake works differently. The button or switch is an electrical control rather than a direct connection between the driver's hand or foot and the brake mechanism. What happens after the switch is operated is determined by the vehicle's electronic and mechanical systems.
So can you use that button to stop a moving vehicle in an emergency?
It depends on the vehicle
There is no single answer that applies to every vehicle equipped with an electronic parking brake (EPB).
Some manufacturers provide an emergency-braking function that can be activated by operating and holding the parking-brake switch while the vehicle is moving. Some vehicles use their electronic braking and stability systems to manage how the brakes are applied. Others may operate differently.
Do not assume that your electronic parking brake works the same way as someone else's.
IMPORTANT: READ YOUR OWNER'S MANUAL
Electronic parking brakes are not all designed or operated the same way. Your owner's manual will tell you whether your vehicle provides an emergency-braking function, how to activate it and what limitations apply. Read and understand these instructions before you need them.
Your owner's manual is the authority for your vehicle. Read it before an emergency, not during one.
Why not just press the button?
An electronic parking brake replaces that mechanical control with an electrical switch. What happens after you operate the switch is determined by the vehicle's design and its electronic and mechanical braking systems.
This distinction matters because suddenly applying the rear brakes hard enough to lock the rear wheels could cause the vehicle to become unstable. A vehicle that loses rear-wheel traction can begin to rotate, particularly if the driver is steering at the time.
Some modern vehicles can use their electronic braking and stability systems to help control an emergency application of the parking brake. Others may operate differently. You cannot determine what your vehicle will do simply by looking at the parking-brake switch.
What if the service brakes fail?
A complete loss of braking is unusual, but it is something every driver should know how to respond to.
First, don't panic. Keep your attention on controlling the vehicle and look for a safe place to stop.
Take your foot off the accelerator and, if possible, select a lower gear. This can increase engine braking and reduce the vehicle's speed.
Do not turn the ignition or vehicle power off while you are still moving. Doing so may disable or reduce the operation of systems you need to maintain control of the vehicle.
If the brake pedal suddenly feels ineffective, press it firmly again. Depending on the nature of the problem, a second application may restore some braking ability.
If your vehicle has an electronic parking brake with an emergency-braking function, follow the procedure specified in your owner's manual. Do not assume that a brief press of the button will activate emergency braking. Some manufacturers instruct the driver to pull up and hold the switch while the vehicle is moving.
Continue steering the vehicle toward a place where you can stop safely. Avoid unnecessary steering movements and remember that even reduced braking is better than no braking at all.
Don't wait until the brakes fail to learn how it works
It may be tempting to try the parking-brake switch while driving slowly just to find out what happens. Don't.
Even at low speed, deliberately activating a parking brake that you do not understand could cause an unexpected braking or stability event.
Instead, find the section of your owner's manual that describes the electronic parking brake and read it. Look specifically for instructions concerning emergency braking while driving or emergency braking with the parking brake.
Knowing beforehand whether your vehicle provides an emergency-braking function—and knowing exactly how the manufacturer says to activate it—could be valuable information in an emergency.
The parking brake is not a substitute for the service brakes
The parking brake is not intended to replace the vehicle's normal braking system. It is primarily there to keep a parked vehicle from moving.
The fact that some electronic parking brakes can also provide emergency braking does not mean that they are a second, independent braking system that can always be used in the same way as the service brakes.
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