The brake will also release automatically with the ignition switch ON, the transmission in gear and the driver pressing the accelerator pedal (drive-away mode).

If the switch is held up while vehicle speed is greater than 6 mph, the control unit will send a brake-apply request to the ABS control unit and the hydraulic brakes will be applied. Once stopped, the hydraulic brakes will release and the EPB will apply to hold the vehicle.

Depending on how the driver's preferences have been programmed, the brake may apply automatically when removing the key from the ignition switch. To override this, the brake switch down must be held down (release EPB) when removing the key.

The control module remains "awake" for 20 minutes after key-off. During this time, it will still respond to switch commands.

Operating the switch will "awaken" the control unit from its sleep mode. If brake release is requested, or if brake apply is requested and the brake is already applied, the control unit will ignore the request but illuminate the parking brake light on the instrument panel. It will then go back to sleep when the switch is released. If brake apply is requested and the brakes are not applied, it will apply the parking brakes and go back to sleep after three minutes.

The cable force sensor inside the actuator housing allows the control unit to know when to turn off the motor when applying or releasing the brakes. After the brakes are applied, the control unit monitors that sensor for 20 minutes (or any time it's awakened), and it will run the motor as needed to maintain the programmed brake force. Sometimes these adjustments can be heard long after the vehicle is shut off.

Audi/Volkswagen

Some Audi models and the Volkswagen Passat have an ATE EPB system that uses a motor mounted on each rear caliper. The motor and its transmission can be removed without removing anything else, but because the control unit measures brake clamping force, a scan tool is needed to release, disable and initialize the system when installing the motor, when installing new brake pads and when bleeding the brakes. ATE makes an aftermarket tool for this called the EST that plugs into the OBDII connector and allows remote operation of the system.

From the driver's seat, the EPB can only be released when pressing the brake pedal. It also can be used as an emergency brake while driving, and it can be used as a hill-holder, too. With the vehicle stopped and the brake pedal pressed, pulling the EPB switch applies the parking brake. The driver can release the switch and brake pedal and the EPB will release automatically when the accelerator pedal is pressed.

The parking brake indicator light on the instrument panel is used to communicate several messages to the driver:

• The EPB light will illuminate any time the EPB switch is turned ON.
• When the EPB is engaged with the ignition switch turned OFF, the EPB light will turn ON for 30 seconds.
• If the light blinks continuously after turning the EPB switch ON, the brake has not attained sufficient clamping force to hold the vehicle. This may be due to vehicle incline: look for a notification on the instrument panel display.
• If a malfunction is detected in the EPB system, the yellow warning light will illuminate and a notification will appear on the instrument panel display.

Whether you work on these vehicles or not, they are the first of many that will be equipped with EPBs. Because EPB systems literally have a mind of their own, knowing how they think and work is not only a matter of convenience, it's also a safety issue. More information can be found in the vehicle owners' manuals, at the car manufacturers' Web sites and at the system suppliers' Web sites.