Editing Electronic throttle control (section)

== Failure modes ==
There is no mechanical linkage between the accelerator pedal and the throttle valve with electronic throttle control. Instead, the position of the throttle valve (i.e., the amount of air in the engine) is fully controlled by the ETC software via the electric motor. But just opening or closing the throttle valve by sending a new signal to the electric motor is an open loop condition and leads to inaccurate control. Thus, most, if not all, current ETC systems use closed loop feedback systems, such as [[PID control]], whereby the ECU tells the throttle to open or close a certain amount. The throttle position sensor(s) are continually read and then the software makes appropriate adjustments to reach the desired amount of engine power.

There are two primary types of [[Throttle Position Sensor]] (TPS): a [[potentiometer]] or a non-contact sensor [[Hall effect sensor|Hall Effect sensor]] (magnetic device). A [[potentiometer]] is a satisfactory way for non-critical applications such as volume control on a radio. However, these devices which are mechanical in nature can wear, get contaminated by dirt and dust and can cause erratic operation in a motor vehicle. The more reliable solution is the magnetic (or optical) coupling, which makes no physical contact, so will never be subject to failing by wear. This is an insidious failure as it may not provide any symptoms until there is total failure. All cars having a TPS have what is known as a 'limp-home-mode'. When the car goes into the limp-home-mode it is because the accelerator, engine control computer and the throttle are not connecting to each other in which they can function together. The engine control computer shuts down the signal to the throttle position motor and a set of springs in the throttle set it to a fast idle, fast enough to get the transmission in gear but not so fast that driving may be dangerous.

Software or electronic failures within the ETC have been suspected by some to be responsible for alleged incidents of [[unintended acceleration]]. A series of investigations by the U.S. [[National Highway Traffic Safety Administration]] (NHTSA) were unable to get to the bottom of all of the reported incidents of unintended acceleration in 2002 and later model year Toyota and Lexus vehicles. A February 2011 report issued by a team from [[NASA]] (which studied the source code and electronics for a 2005 Camry model, at the request of NHTSA) did not rule out software malfunctions as a potential cause.<ref>{{citation |url=http://www.nhtsa.gov/UA |title=NHTSA-NASA Study of Unintended Acceleration in Toyota Vehicles |publisher=National Highway Traffic Safety Administration |date=15 April 2011 |access-date=25 November 2013 |url-status=dead |archive-url=https://web.archive.org/web/20110320003514/http://www.nhtsa.gov/UA |archive-date=20 March 2011 }}</ref> In October 2013, the first jury to hear evidence about Toyota's source code (from expert witness [[Michael Barr (software engineer)|Michael Barr]]) found Toyota liable for the death of a passenger in a September 2007 unintended acceleration collision in Oklahoma.<ref>{{cite news |url=https://www.latimes.com/business/la-xpm-2013-oct-25-la-fi-hy-toyota-damages-20131026-story.html |title=Toyota settles acceleration lawsuit after $3-million verdict |first1=Jerry |last1=Hirsch |first2=Ken |last2=Bensinger |work=Los Angeles Times |date=25 October 2013 |access-date=24 November 2013}}</ref>