Tech Feature: Electric/Electronic Parking Brakes

Tech Feature: Electric/Electronic Parking Brakes

The current emergency/parking brake is the most unused device on a vehicle equipped with an automatic transmission. But, the electrically actuated parking brake is changing the parking brake into a multi-purpose mechanism on modern vehicles. Using an electric motor to apply the parking brake results in the mechanical linkage being eliminated from the vehicle passenger compartment.

figure 1: the actuator is made up of a gear train that rotates a splined screw nut to retract the two cables. it also contains a mechanical release feature.The electric motor applies the shoes in the drum hat of the rear disc brake or the caliper parking mechanism. It can be applied manually by the driver or automatically as an anti-theft deterrent when the vehicle is parked and locked. The brake will automatically release when the vehicle is placed in gear.
This can be an important feature to the all-wheel drive used on sedans and crossovers. The electric application of the parking brake can be used to hold the vehicle and prevent it from rolling backwards on a hill. The hill-holding feature is incorporated into the Electronic Stability Control (ESC) and uses sensor information from the Controller Area Network (CAN) bus.

figure 2: a motor and gear train attached to the rear caliper parking actuator.An electric parking brake can come in two configurations. Both actuate conventional parking brake mechanisms.  

Type 1 is an electric motor and mechanical actuator mechanism mounted to the body of the vehicle. The actuator is connected to the cables for the rear drum-in-hat brake shoes or caliper parking brake mechanism. When the parking brake actuator is activated, the actuator retracts the cables attached to the caliper or the shoe mechanism.  
Continental Teves manufacturers a cable-retracting unit used on many vehicles such as Mercedes Benz, Jaguar and Land Rover. A switch is connected to the actuator. The actuator can also be connected to the CAN bus. The actuator is made up of a gear train that rotates a splined screw nut to retract the two cables. It also contains a mechanical release feature as shown in Figure 1.

Type 2 uses a motor and gear train attached to the rear caliper parking actuator as shown in Figure 2. This second type will most likely become the standard in that it eliminates the cables to actuate the parking brake and making one electrical and one hydraulic connection at the caliper. The switch is connected to a control module or to the anti-lock brake system (ABS). 

The Bosch Automatic Parking Brake (APB-M), Continental Teves and TRW integrated Electric Parking Brake (EPB) systems incorporate a hill-holding feature.  If the vehicle stops on an incline, the system maintains braking until the driver has released the brake pedal and the vehicle moves forward. The parking brake can be automatically applied when the vehicle is parked and unoccupied. When the vehicle is started and placed in gear and moves forward, the parking brake is again automatically released.

All systems use a separate Electronic Control Unit (ECU) or the ECU function is incorporated into the ABS system. Whether the controller is separate or incorporated into the ABS system, the ECU electronics will contain a bi-directional motor controller circuit connected to the brake actuator motor. Manual apply input will come from the parking brake switch that is directly connected to the controller or ABS.  

CAN bus information from the ESC program is responsible for the hill-holding control of the actuator. Shared information for the hill holding feature comes from the yaw, incline and acceleration sensors along with gear selection and steering wheel position. The electric parking brake ECU monitors the operation of the parking brake motor and places that information on the CAN bus. Figure 3 is a block diagram of the controller and motor.


Most GM vehicle with the TRW cable actuated system have the motors located in the passenger-side rear wheel well behind an access panel. On most Ford and Jaguar vehicles, the actuator is in the trunk. It is possible to release the system if the battery is dead. Most of these procedures are outlined in the owners manual that is in the glove box.

If you are doing a brake job on an electric parking brake vehicle like some Audi and VW vehicles, you will need a scan tool with the proper software for the parking brake system or a dedicated tool to reposition the cable retractor or the calipers.

Do not try to reverse polarity or force a piston back. You could damage the gears or motor.

You May Also Like

Axle Torque Procedures

Guessing the correct torque setting is a bad idea.

The physics of all threaded fasteners are the same. As the bolt and nut are turned, the spiral threads convert rotational force into a linear force that creates clamping loads. When a threaded fastener is tightened, it stretches. Since metal is elastic, even greater clamping loads are generated. The threads also generate friction that keeps the assembly together. This especially applies to wheel bearings and axle nuts.

Gen 1 Wheel Bearings

Removing and installing these bearings requires the correct tools and patience.

Tapered Wheel Bearings

Here’s what you should know as a technician when servicing tapered wheel bearings.

Understanding Passive Wheel Speed Sensor Operation

Passive types of wheel speed sensors are still used in many applications so understanding their operation is important.

Threadlocking Compounds For Vehicle Corners

To get the most out of these “liquid” tools, you first need to know how they work.

Other Posts

Please Take Our Brakes/Rotating Electrical Survey

By entering, you’ll have a chance to win a $100 gift card or one of 10 $25 gift cards!

ADAS False Activation Evolution

The logic behind most ADAS warnings or corrections is to examine the plausibility of the situation.

Understanding ADAS: Blindspot Detection Systems

With the right tools and service information, it is possible to resolve a customer’s complaint. 

Read the March ShopOwner Digital Edition Now

Each issue is free to download and read, priceless in business value for your operation.