Malfunction Indicator Lamp
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A Malfunction Indicator Lamp (MIL) is an indicator of the internal status of a car engine. It is found on the instrument console of most automobiles. When illuminated, it is typically either a red or amber color. On some vehicles, the light has two stages: steady amber (indicating a fault such as loose gas cap or O2 sensor) and flashing red (indicating a severe fault, such as catalytic converter problems or engine misfire).
The Malfunction Indicator Lamp is usually labeled with the text Check Engine, Service Engine Soon, Check Engine Soon, or a picture of an engine, and can illuminate for any of a very large number of reasons. Typically, the reason is not serious enough to affect drivability of the vehicle. Common causes include: loose gas cap, vehicle due for scheduled maintenance (i.e. oil change), or problems with the emission control system (i.e., charcoal canister or oxygen sensor).
This light became required on passenger cars due to emission control legislation in California, with the intention that the light would illuminate if there was a problem which would cause the vehicle to have excessive pollutant emissions. The owner would be aware that the emission control system needed to be serviced, and would be prevented from renewing their registration in the state of California.[citation needed]
The Malfunction Indicator Lamp can also illuminate for reasons which may affect drivability, so it is advisable that one have the vehicle examined by a mechanic at one's earliest convenience. A preliminary diagnostic check can be performed by retrieval of the fault code which has caused the light to illuminate. The cost of hooking up a diagnostic computer to retrieve the trouble code varies greatly, costing as much as US$99.[citation needed]
Once a fault code has been pulled, the technician will have a better idea of what the problem may be. These codes are seldom specific, but instead tend to relate to a system of complex parts, thus requiring further diagnosis. Said diagnosis will require paying the hourly labor fee of a skilled technician.[citation needed]
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[edit] Hard code vs soft code
If the cost of replacing a non-essential part seems exorbitant, one may choose to "clear" the code by having the computer reset. If the problem reoccurs, the light will come back on. Sometimes the light goes off on its own — this indicates a "soft code", which usually refers to a temporary non-serious problem. Even though the emission system typically does not affect anything more than gas mileage, problems will trip a "hard code", requiring a reset. One can attempt the reset themselves, either by removing (and reinserting) the proper fuse, or by temporarily disconnecting the battery. However, this will not work on all vehicles, and disconnecting the battery may reset other systems as well (such as the idle). When the car no longer starts, you will not have to worry about the light. In the states of CA, MA and NY, vehicles with the "check engine" light on will not pass annual inspection.[citation needed]
[edit] "Trouble" indicator
Be advised that on older vehicles, the unlabeled red light ("trouble" indicator) should NEVER be ignored, as said light typically only comes on just prior to a major breakdown of the engine (i.e., overheating due to low oil or coolant). Since this "trouble" indicator only indicates severe problems, it is not a true MIL. A "trouble" indicator may be a single red light, or several red lights indicating oil pressure, temperature, battery, and brake. As these lights were meant to replace gauges which the average driver found confusing, they are commonly referred to as "idiot lights." If an "idiot light" comes on, it is often advisable to immediately stop your vehicle and have it towed to prevent further damage. As the Malfunction Indicator Lamp typically works as an early warning of a non-essential problem, it would not be considered an idiot light.
[edit] Odometer triggering
Some vehicles made in the late 80s and early-to-mid 90s have a MIL that illuminates based on the odometer reading, regardless of what is going on in the engine. For example, in several Mazda models, the light will come on at 80,000 miles and remain lit without generating a computer trouble code. This was done in order to remind the driver to change the O2 sensor. In such cases, the only way to fix the problem is to make a physical adjustment inside the dashboard, such as removing a screw from one location and putting it in another location (replacing the O2 sensor alone will not cause the light to turn off).[1] The light will illuminate again at subsequent 80,000 mile intervals, at which point the fix must be repeated.
[edit] Ethanol
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Please help improve this article or section by expanding it. Further information might be found on the talk page or at requests for expansion. This article has been tagged since January 2007. |
Higher amounts of ethanol than the engine can handle efficiently may also trigger the Malfunction Indicator Lamp (see E85).
