Like HowStuffWorks on Facebook!

How Electronic Throttle Control Systems Work

ETC Failsafe Modes

Like most complex systems, electronic throttle control systems have a number of failsafes. These are designed as redundancies and backups to keep the system running, or provide a safe shutdown if something goes wrong.

Generally speaking, at the first sign of a problem, most electronic throttle controls are designed to close the throttle and return to idle. So, for example, if the engine control unit detects a problem with a sensor, the system reverts to idle, preventing the throttle from opening.

Similarly, there are a number of redundancies built into the system. For example, just one sensor isn't used to detect driver inputs or other factors. Each sensor position uses two sensors. If a sensor malfunctions, or the two sensors in a given position report different readings, the system closes the throttle, idling the engine.

What about outside interference causing power surges or short circuits? Most systems use a smart throttle motor. The throttle motor is the final gatekeeper that throttle signals need to go through before the throttle actually moves. If the throttle motor detects voltage or signals that didn't come from the engine control module, it's designed to shut the engine down. If electromagnetic interference were strong enough to affect electronic throttle controls, the throttle control system is designed to shut down, not surge ahead.

That's not to say that electronic throttle control systems are problem-free; rather, they've been designed with a number of failsafes that, if working properly, should prevent unexpected engine surges and acceleration.

Still, in the wake of new consumer awareness about unintended acceleration and questions about electronic throttle controls, car makers are adding another failsafe: brake overrides. These systems, which are already available on a number of cars from German manufacturers, allow driver inputs to step in and override the throttle system. So, if the system malfunctions somehow and the throttle opens on its own, stepping on the brakes will close it.

Electronic throttle control is just one of the electronic components under the hood. Learn about others by reading the links on the next page.

More to Explore