Though it might vary somewhat by car (always check your manual for an explanation of your dashboard lights), most automobiles have basic warning lights for things such as brakes, oil, battery and temperature, along with the "check engine" light. If you see "brake" or "ABS" light up on your dashboard, it means something's wrong with you braking system. When the ABS light is on, your antilock brakes might turn themselves off until you fix the problem (though your regular brakes still work even with the ABS off). When the regular brake light is on, it might mean your parking brake is engaged; it also can mean something's wrong with the hydraulic pressure in part of your braking system or that you're extremely low on brake fluid. If both the ABS and normal brake lights are on at the same time, you might not even want to drive your again car until a professional looks at it.
An illuminated oil light usually means your engine has low oil pressure or is running out of oil; low pressure might mean you have a broken oil pump, clotted oil or a clogged filter. If your car's battery light turns on, your battery might be low or the alternator might not be producing enough power to charge the battery and run the car. If that's the case, the battery is bearing the brunt of the load. When your car's temperature light (which often looks like a thermometer symbol) turns on, your engine is overheating. An overheating engine is serious, and something you should handle immediately.
The more general check engine light could signal a problem with the emissions system, a loose gas cap, a spark plug issue or even moisture someplace in the engine it should not be. Since 1996, the U.S. Environmental Protection Agency (EPA) has required cars and trucks weighing less than 8,500 lbs (3,856 kilograms) to have an on-board diagnostics system that lights up when something isn't working properly with a "check engine" warning on your dashboard. The issue can range from the minor loose gas cap to more serious engine problems. If the light flashes continuously, the problem is serious and should be checked out immediately.
Occasionally, sensors trigger a warning light unnecessarily, but the light usually shuts off again quickly. When the light turns off by itself, it's okay to ignore the fact that it turned on in the first place. When you first start your car, all of the dashboard warning lights turn on for a few seconds -- just so you can make sure they work. That's not a cause for concern; but if one of them doesn't turn on at all, it means the bulb is out and should be replaced. And if any light turns on and stays on, have the car checked by a professional to pinpoint the problem.
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