Idiot light is a mildly derogatory term that 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, idiot lights consist of an illumination source (usually an incandescent light bulb or an LED) with an explanatory symbol or text label. An "idiot light" will only turn on after a malfunction has occurred, providing no warning in advance, nor details of the malfunction's extent afterwards.

Use in cars

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). The "idiot" factor refers to the popular belief that the car maker decided that most drivers lack the technical expertise to properly understand gauges, and the car maker preferred to cut costs by not including such instruments. In contrast, an oil pressure gauge allows the driver to see oil conditions at all times, allowing problems to be monitored before they become critical.

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, which indicated low oil pressure, overheating and carburetion problems without distinguishing between them.

In modern electronic fuel-injected cars the "check engine" light usually only indicates minor problems that do not require immediate attention. It might, for instance, indicate that the fuel-injection computer has detected a reading from a 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 eventually damaged. Mechanics often refer to this state as "limp-home mode." A comprehensive instrument panel includes both gauges and alert lights: gauges to give a precise indication of coolant temperature, oil pressure, charging current, and voltage; and lights to catch the driver's attention when readings approach the "danger zone".

References