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How Automotive Warning Lights Work


What Trips an Automotive Warning Light?
In her Automotive Technology class at Wenatchee Valley College in Wenatchee, Wash., Amber Horn uses a scan tool to check over various systems in a 1995 Ford Windstar on April 14, 2004.
In her Automotive Technology class at Wenatchee Valley College in Wenatchee, Wash., Amber Horn uses a scan tool to check over various systems in a 1995 Ford Windstar on April 14, 2004.
AP Photo/Kelly Gillin

Like we mentioned earlier, sensors in the car notify the driver of a potential, or already existing, problem. When a check engine light comes on, there may be a problem with the emissions system. The light can be tripped by something as simple as a loose gas cap, or could mean there's a problem with the spark plug wires, a deteriorated fuel injector O-ring, faulty oxygen sensors or possibly that an area of the engine has water in it where moisture should not be.

If the brake light is on, the parking brake may be set, misadjusted, or something more serious may be occurring that involves a trip to the auto maintenance shop. If the light comes on when you apply the brake or stays on continuously, the hydraulic pressure has been lost in one side of the braking system or brake fluid in the master cylinder is very low. Either way, some type of vehicle maintenance will be required. If the ABS and the brake warning light are on at the same time, the vehicle may not be safe to drive and should be taken to an automotive maintenance shop.

When the battery light is on, it usually means that the alternator is not producing enough electricity to supply the car with electricity and to charge the battery at the same time. This means the car's battery is handling the full load of the ignition system, fuel pump, radio, heater, lights and other electrical functions. The battery light can also be triggered if the belt that spins the alternator is slipping, broken, or has come off of the pulley completely.

A temperature warning light is tripped when the engine is overheating. An overheated engine is always a serious issue and may require car maintenance right away. Sensors in the cylinder head will turn on the warning light if it gets too hot, or coolant sensors may notify the driver if the fluid levels are too low for the system to function properly.

The oil warning light will come on if the sensor determines there's low oil pressure, or if the oil level in the pan gets too low. If there's enough oil in the engine, then low oil pressure is the cause of the warning light, which can come from a worn or broken oil pump, clogged oil in the crankcase's pick-up screen or a plugged oil filter.


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