Electric handbrakes: what they are and how they work

The electric handbrake, also known as the electric parking brake (EPB), is an innovative tool that was first installed in the 2001 BMW 7 Series. It has been slowly replacing the standard manual variant ever since. Their basic functionality is similar, but instead of pulling a lever, like for a manual handbrake, the driver pushes a button. An electronic control unit (ECU) then activates the holding mechanism that applies the brake pads to the rear wheels.

Design and function

How electric handbrakes work tends to be very similar. Electronic handbrakes have an interface, usually a button, by which the driver can activate them, as well as an actuator mechanism. There are two main types of mechanisms by which an EPB may be engaged, those based on cables and those on calipers. Cable puller systems operate via a parking brake cable that activates the brakes upon being pulled taught. Electric parking brakes with caliper integrated systems instead use a brake caliper actuated by a motor that engages the brakes.

In both cases, the signal from the interface is routed through an ECU. This may either be part of the electric parking brake or integrated into the electronic stability control ECU.

Additional features

Electric parking brakes have additional features that distinguish them from regular handbrakes. Due to their electronic nature, the electronic handbrakes are usually associated with an indicator light on the dashboard showing that the brake is engaged. Because the entire device is electronic, the driver can tell more easily that the car is securely held in place than with a manual parking brake.

EPBs can also come equipped with an auto hold or a hill start function. Electronic parking brakes with auto hold prevent cars from rolling away while standing still or as the driver is about to get going. Hill start or hill hold functions operate in a similar manner but are specifically intended to prevent the car from rolling away while starting on a slope.

How to use an electronic handbrake

How the EPB gets activated can vary from car to car, but typically it involves pressing the appropriate button and sometimes involves depressing the brake pedal as well. Cars with manual gear selection usually require you to depress the clutch as normal and then engage the gas pedal as you release the former. Electric handbrakes that disengage automatically don’t even require a press of the button when starting.

A hill start with an electric handbrake is quite simple, though the exact way to disengage the electronic handbrake when starting the car on a slope varies. If the EPB supports hill starts, it will automatically disengage after a few seconds from the point of depressing the clutch and activating the gas pedal. Automatic cars naturally forgo the use of a clutch pedal. Electronic parking brakes that don’t have a dedicated hill start function require the driver to find the right moment to press the button that releases the parking brake.

Advantages over standard handbrakes

Unlike standard handbrakes, electric parking brakes don’t require additional muscle power to use. They activate with the pressing of a button and lock the car securely in place. The risk of accidentally applying too little force on the brakes and the car rolling away later is eliminated. Caliper integrated systems have the additional benefit that they are less prone to frost and the braking cables wearing out. They also save space in the interior, as there is no need for the lever mechanism. Their electronic nature also allows the system to warn drivers of malfunctions by lighting up the “Service Handbrake” indicator on the dashboard. Manual handbrakes usually require a severe malfunction or an inspection of the underbody to detect potential problems. Hill starts are also simpler and safer regardless of whether the device supports them explicitly.

Problems with electronic handbrakes

While electric parking brakes have many features that make them safer and more efficient than manual handbrakes, they do come with their own risks. Being an electronic unit, the EPB is prone to malfunction when the voltage of the car’s electric system is low or other issues with the onboard network crop up. A flat battery can prevent the brakes from receiving signals at all, leaving the car stuck in place. Malfunctions or damage to the wires or fuses can also spill over onto the electronic parking brake: opened, shortened, or broken wires connected to the parking brakes ECU can prevent it from working properly. Other common problems include jamming of the electric parking brake’s actuator, electrical faults in the ECU, miscommunication between different modules of the EPB, malfunctions of the brake pedal switch or gear stick switch, or corroded braking cables in cars that have cable puller systems.

Electric parking brakes sometimes have manual releases for these situations, but if the EPB won’t release manually or automatically and you can’t easily determine the issue, a diagnostic tool is required to figure out what went wrong with the device. Electric handbrakes are sophisticated mechanisms and not easily repaired by laypeople. An expert technician at a garage equipped to service your particular brand and make of car is usually required to fix any issues that crop up. This counts for replacing of the brake pads and of course any work on the ECU itself as well.

Conclusion

All in all, an electric parking brake trades ease of repair for a simpler activation and higher safety. The ease of use, additional safety, and the saving of space mean that EPBs will only become more common in the future.

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