How Brake Override Systems Work

Brake Override System Technology

The technological breakthrough that made brake override systems possible is the same thing that made so many of our safety systems possible: a fully integrated electronic system. Once BMW built the system for its electronic throttle, or "drive-by-wire" system, which relied on electronics rather than mechanical or hydraulic controls, it was simple to add a brake override system, too. The wires were already there, and so was the computer.

As Nick Cappa, the engineering and technology spokesperson for Chrysler, said, "Electronic controls gave automakers the opportunity to operate multiple systems with one action." So if it wanted, an automaker could make the dome light come on when you turned on the radio, since it's all connected with sensors that relay information to the computer. Or, more practically, the system could sense a problem with the brake and gas pedals and safely slow the car down.

In the case of brake override systems, the system requires sensors at the brake and gas pedals, a computer to make decisions for what the car should do and wiring to connect it all. If it detects a problem, like the driver holding the brake while the car is speeding up, there are several ways for the computer to engage the brake override and "derate" the engine, as the auto guys call the reduction of power. It can:

  • Adjust the throttle position
  • Reduce the amount of fuel getting to the engine
  • Change the timing

Which course of action the car takes depends on what the manufacturer has programmed the computer to do when the gas and brake pedals are both pressed. No matter which method the car uses, the goal is the same -- the car will slow to a stop.

Toyota, for example, uses accelerator pedal sensors, brake light switch circuitry and vehicle speed sensors to detect when a vehicle may be going out of control. If the vehicle is traveling at 5 mph (8 kph) or more and the brake pedal is pressed for a half second or more, then the system puts the engine in idle to slow it down. The half-second allowance keeps the system from trying to stop the car during hill starts or when the driver is rocking the car to find traction in snow or mud.

This is all fancy stuff, but what are the benefits of a brake override system? Read on to find out.