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Electronic Parking Brake

Copyright AA1Car.com

More new vehicles are being equipped with Electronic Parking Brakes or EPB. The parking brake is just one more system that has been integrated into the onboard electronics to provide a smarter, safer and more convenient means of braking the wheels under a variety of situations.

Advantages of the Electronic Parking Brake

An electronic parking brake eliminates the bulky parking brake lever or pedal inside the car. An electronic parking brake only needs a small switch or button that can be located anywhere and activated by fingertip. It requires no effort, and no thought in the case of a smart EPB system. The smart EPB system automatically applies the brake without driver input when the vehicle stops moving or the transmission is placed in Park.

An electronic parking brake can also have a built-in intelligent release function so that it is not accidentally left on when the transmission is placed in gear. The EPB can also be used to provide a "hill holding" capability on vehicles with manual transmissions so the car doesn't roll backwards, or forwards, when stopped on a slope.

EPB can also function as an emergency brake should the hydraulic brakes fail -- although when applying the rear brakes only, it can take a long time to slow down or stop a speeding vehicle. Even so, it's better than no backup at all.



Electronic Parking Brake Applications

Electronic parking brake applications on import vehicle brands include 2000 and up Audi A4, A5, A6 & A8, 2002 and up BMW 5 and 7 Series, and Z4 models, 2001 and up Mercedes models with Sensotronic Brake Control, Jaguar S-Type, XF and XJ, 2003 and up Volkswagen Passat, and 2010 Subaru Legacy and Outback. Domestic applications include 2003 to 2006 Lincoln LS,

2011 Ford Mustang, 2008 Buick Lacrosse, and 2009 Cadillac CTS. Many more models are expected to be equipped with electronic parking brakes in the years ahead.

GM and Ford Cable Actuated Electronic Parking Brakes

On current models, General Motors and Ford have both opted to use a cable-style electronic parking brake system. A similar setup is also used by Lexus on their LS 460 models, Jaguar on their X-Type and XJ models, BMW on their 5 and 7 Series, and Z4, and on Land Rover models with EPB.

The rear brakes on these applications are applied by pulling cables (like a mechanical parking brake), but an electric motor and ratcheting assembly are used to apply the force rather than a hand lever or foot pedal. These systems have a control module to operate the EPB motor, with input coming from a driver operated EPB switch in the passenger compartment. The module may also receive inputs from other onboard control modules that may request application of the parking brake depending on operating conditions (as when parking the car, holding the car on a hill when it is stopped, or for emergency backup braking).

On the Cadillac CTS, the EPB actuator and control module are one unit, which is located on top of the rear subframe. On the Lincoln LS and Jaguar models, the EPB actuator is located inside the trunk behind the rear seats, and the module is mounted inside the trunk near the left fender.

With these cable-actuated EPB systems, no special service procedures are required when servicing the rear brakes other than to make sure the parking brake is fully released prior to working on the calipers or replacing the pads. This is important to know because the parking brake has to be released before the calipers can be removed to change the rear brake pads.

On the Cadillac CTS, the EPB can be released with a scan tool, or released manually by turning the ignition on (engine off), placing the transmission in Park (or neutral with a manual transmission), then pressing and holding the EPB switch for 5 seconds. When the parking brake warning lamp starts to flash, release the EPB switch, then immediately press and release the switch once more to deactivate the parking brake.

On the Lincoln LS, the electronic parking brake is released by turning the key on, pressing on the brake pedal and pushing the EPB switch down. The brake warning lamp will go out when the EPB is released. The EPB system will also automatically release if the transmission if shifted out of Park while the key is on. But on Lincoln LS models up to 2007, the electronic parking brake only releases when the transmission is shifted into Drive (not Reverse). You must be holding your foot on the brake otherwise it won't release until you press down on the gas pedal.

vw electronic parking brake

Audi, VW and Mercedes Electronic Caliper Parking Brakes

On the Audi, VW and Mercedes EPB applications, a different setup is used. The rear calipers are fitted with small electric motors and reduction gears that apply the parking brakes. The gears multiply the force exerted by the electric motor to force the caliper piston out and clamp the pads against the rotor.

With the European electric motor actuated EPB systems, service procedures can be more complicated. The electronic parking brake system can be cycled on and off using the EPB switch, or it can be deactivated with a scan tool or special EPB service tool.

On the European and domestic EPB systems, a scan tool with the appropriate software and capabilities is required for reading and clearing codes, and for running system self-checks (such as applying and releasing the parking brake).



Electronic Parking Brake Problems

Like any electronic system, problems can occur in the EPB if wires or circuits between the EPB switch, module and actuator are shorted, open or develop high resistance. Common faults such as an open fuse or low system voltage can prevent the system from operating normally. Most of these systems can self-diagnose gross faults, and will set a code and flash the brake warning light or display a "Service Parking Brake" message if a problem is present. A scan tool must then be used to read the code(s).

If a major system component has failed (such as a control module or actuator), the parts will have to be sourced from the new car dealer due to the fact that these systems are still relatively new and low in number. As time goes on, some of the EPB components will likely become available though automotive parts stores.

If the parking brake fails to release automatically or manually, it could be stuck on for a number of reasons:
* There is an electronic fault with the EPB control module.
* The parking brake electric actuator motor has failed or is jammed.
* The gear shift selector switch or brake pedal switch are faulty.
* There is a communication fault between either of these switches and the EPB module.
* One or both parking brake cables are corroded and sticking.

If you have a Lincoln LS and see a "SERVICE PARKING BRAKE" warning in the instrument panel message center, it could indicate a real problem with the system, or a false problem. The EBP module on the Lincoln is very sensitive to any electronic noise in the vehicle's electrical system. In some cases, this can be caused by a failing ignition coil pack or electronic coolant flow control valve. Poor wiring harness connections and grounds can cause a similar problem.

If you want to replace the rear brake pads on a Lincoln LS with electronic parking brakes, hold the parking brake switch DOWN as you turn the key off to prevent the brake from automatically setting. If you don't do this, the parking brake will be automatically applied and you won't be able to get the caliper off the rotor.

ELECTRONIC PARKING BRAKE RECALLS

Electronic parking brakes have proven to be fairly reliable, but there have been some reports of problems on some Jaguar, Subaru and VW models. The only recall issued so far has been one by Jaguar for 2001 to 2003 S-Type models (campaign 04V488000). The recall was issued because the parking brake control module on some Jaguar S-Types would apply the parking brake without any indication or warning while the vehicle is in motion. This causes the rear wheels to lock up and skid. The fix is for the dealer to replace the parking brake control module with a redesigned module at no cost to the vehicle owner.

The related Jaguar service bulletins are:

JTB-00208, issued 11/22/2010 which covers Jaguar electronic parking brake re-calibration procedure.

20608 issued 12/01/2005 which covers the electronic parking brake actuator diagnostic codes c1784, c1785, c1786, c1799, c1801, c1802, c1803

20604 issued 08/01/2005 which covers premature parking brake pad wear or the brakes binding due to electronic park brake system being miscalibrated.



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