Tell-tale (automotive)

Idiot lights

The term idiot light refers to a simplistic method of displaying information about a system (e.g. an engine, or a piece of factory equipment). Usually found in display panels, such as an automobile dashboard, they consist of an illumination source (usually an incandescent light bulb or an LED) with an explanatory symbol or textual label. The usual method of operation is that the light is lit when the condition indicated comes into an effect.

An example of an "idiot light" is an oil warning indicator in an automobile. When an oil related problem is sensed a light is illuminated on the car's dash (usually in red) for driver note. The "idiot" factor comes to play in such a case either because the car maker decided that most drivers are too idiotic to be able to read a full oil pressure gauge, or the car maker was too cheap to include such an instrument. Either case constitutes idiocy from the standpoint of many auto professionals, as an "idiot light" will only come on after a problem has occurred, with no advanced warning. In contrast, an oil pressure gauge allows the driver to see oil conditions at all times, allowing for the chance to note problems before they become critical.

Graphical idiot lights

Historically, the "check engine" light, which is usually an orange light overlaid with a symbolic representation of an engine, is also called an "idiot light". This is particular to some older car models, which have an unlabeled red light ("trouble" indicator). In particular, early 1980s Fords without the instrument option had only one light, covering low oil pressure, overheating and carburetion problems - basically, this indicator means that the engine is about to break.

In modern cars the sole "check engine" light mostly means noncatastrophic problems, so it is not exactly "idiotic" in the sense described above - in fuel-injected cars, this typically means that the fuel-injection computer has detected a weird reading from a (possibly failed) sensor and has changed to open loop mode, meaning that the computer is no longer adjusting the engine's parameters according to conditions and exhaust. If this is the case, performance and gas mileage will suffer and the catalytic converter may be damaged. Mechanics often refer to this state as "Limp Home mode", since the computer has alerted the driver that there is a problem which should be addressed as soon as possible.

Still, getting any further details about the state of the engine requires a special tool ranging from a hairpin to a diagnostic scanner. By connecting a specific pair of pins on the diagnostic connector, most fuel-injected American cars will indicate the problem by flashing a code sequence with the Check Engine light; flashed signals are occasionally but not usually misleading.

Occasionally, people have complained about a check engine light coming on when the problem was that the gas cap was not properly secured. [1] This would be because the car's fuel injection computer recognized that the evaporative control system (which prevents gasoline vapors from polluting the air) was not behaving as intended.

During starting, it is typical for the idiot lights to illuminate, allowing the driver to verify that they operate properly. This initial flashing of many indicator may confuse a beginner driver.

Popular culture

• On the animated TV series The Venture Bros., the existence of idiot lights is parodied in the episode "Careers in Science". Surprisingly, there is only one light (labeled "Problem Light") on an entire space station.