Unlock the secrets of electronic parking brakes - Knowing how Electric Parking Brake systems work is the key to safe system repairs. - Aftermarket Business - Wholesaler, retailer automotive parts
When parking a car, there are two ways to make it stay put: shift into park (or shift a manual transmission into gear) or
set the parking brake. Ideally the driver will do both, but if everything is working properly, either one of these will do
the job.
On most cars, there's a direct mechanical linkage between the driver and the parking brake. However, in a short-but-growing
list of vehicles, an electronic control unit operates the parking brake. The driver can still apply or release the brake with
a button, but these systems can also operate automatically. Some apply the brake in park; some apply the brake when the vehicle
comes to a full stop, when the trunk lid is open or under several other scenarios. To unlock the brakes for service and to
prevent nasty surprises while working on the vehicle, make sure your technician customers know how the control unit "thinks"
and how to disable it.
Electronic Parking Brakes (EPB) are currently made by Continental-Teves (ATE), Aisin and TRW, and soon Siemens VDO, Bosch,
Delphi and possibly others will join the market. Eventually we'll see them on almost any make of car — not just luxury models.
Because the Controller Area Network (CAN) communications bus essentially turns a vehicle into one big integrated network,
we won't have long to wait. CAN is mandatory for 2008 models, and most of the wiring, sensors and switches needed for EPB
already will be installed for other items. The recent development of small but powerful electric motors is the final piece
that makes EPB possible.
Mercedes-Benz TECH NOTES
There are two different types of EPB. One type uses a single motor to pull a cable on an otherwise conventional cable-operated
parking brake system. This is used on the Lexus LS 460, Lincoln LS, Jaguar X-Type and XJ, various BMW models and most Land
Rover models.
The other type has a motor on each rear caliper that mechanically operates the caliper piston. It can be found on Mercedes-Benz
vehicles, Audi A6 and A8 models and the Volkswagen Passat. In each system, the control unit operates the motor in both directions
as needed, just like a window lift motor. In fact, the motor itself may be exactly the same as a window lift motor but with
a transmission to multiply its torque. By themselves, EPB systems are not strong enough to stop the car quickly, but they
will hold it in place.
LEXUS EPB BRAKE ACTUATOR
Repair and maintenance of the caliper-mounted systems is not particularly complicated, provided the tech has the right tools.
However, the cable-puller systems are another story. Removing the actuator from the Jaguar XJ requires removing the fuel tank.
The same job on the Lexus requires removing the rear subframe.
Even if a technician decides not to tackle these jobs, he or she still needs to know how to manipulate the system for normal
maintenance procedures, such as replacing the car's battery or retrieving it from the roll-back.
Jacques Gordon is also technical editor of Motor Age, our 100-year-old sister publication that is written for professional technicians. Jacques, with almost 30 years of automotive experience, has worked for both dealerships and independent shops.
Articles by Jacques Gordon
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