Understanding Tesla's Electronic Parking Brake

Almost all Tesla vehicles come equipped with an electronic parking brake (EPB), a versatile and convenient feature that ensures your vehicle stays safely parked. However, the workings of the parking brake are not as straightforward as one might think, especially when it comes to how it interacts with the vehicle's drive mode.

Does Tesla have a parking brake?

Yes, Tesla vehicles indeed have a parking brake feature that automatically engages when the car is placed in PARK. This is one of the defining characteristics of Tesla's drivetrain, setting it apart from traditional vehicles that rely on mechanical parking pawls. When you initiate the PARK position, here are the actions that take place:

The rear disk brakes are engaged via electromechanical screw drives, clamping onto the brake rotors to ensure the vehicle remains stationary. The red circle with the capital P on the instrument cluster provides a clear visual indication that the parking brake is fully activated. The EPB can also serve as an emergency brake, allowing the rear wheels to be locked and the vehicle to be brought to a safe stop.

Why Tesla lacks a mechanical parking pawl

Tesla’s drive units do not have a mechanical parking pawl because they lack traditional transmissions. Instead, the drivetrain is composed of traction motors with reduction gears (typically 9-10:1) and a simple open differential, followed by half-shafts directly driving the wheels. This setup is both simple and elegant.

Implications of towing a Tesla

Attempting to tow a Tesla, especially one equipped with directly-driven wheels, can be extremely dangerous. For instance, if you unintentionally tow a Tesla with its rear wheels on the ground, you could risk permanent damage to the drive units, possibly even leading to a fire. There is no “Towing Mode” that can resolve this issue.

Details of Parking Brake Mechanics

For Tesla’s BEVs, particularly the Model S/X before the Raven refresh, the rear disk brakes include an additional pair of small calipers driven by electromechanical screw drives for the parking brake function. In contrast, the Model 3/Y integrates the parking brake mechanisms into the existing rear disk brake caliper assemblies, which also include traditional hydraulic brake pistons.

When you first select PARK, the parking screw drives engage, ensuring the rear brakes are enough to prevent the vehicle from rolling. By pressing PARK again, or exiting the vehicle, the clamping force of the screw drives increases, immobilizing the vehicle confidently. The red circle with the capital P on the instrument cluster signifies that the parking brake is fully activated.

Emergency Braking Capabilities

The two-level braking scheme also allows the parking brake to be used safely as an emergency brake. As you might imagine, locking the rear wheels while the vehicle is in motion can be very dangerous. However, the likelihood of needing an emergency brake in a fully-redundant Tesla is very low. Nevertheless, it is always good to know the full capabilities and limitations of your vehicle.

Replacing Rear Brake Rotors

Tesla's Model 3 or Model Y automatically activate their parking brake under various conditions, which can complicate the process of replacing the rear brake rotors if you are not aware of the sequence of operations. Understanding this can simplify the maintenance process.

Conclusion

In summary, the electronic parking brake of a Tesla is a sophisticated feature that enhances safety and convenience. Although it has some unique characteristics that differ from those in traditional vehicles, it is an integral part of the innovative drivetrain design. Maintenance and operation of this feature are critical for ensuring the longevity and safety of your Tesla.

References

For a detailed explanation and visual demonstrations, refer to the following resources:

John Kelly's YouTube video Sandy Munro's analysis of Tesla drivetrains