Have vehicle scanned to determine problem
There are a number of reasons why a check light might be coming on in your car. Once the check engine light comes on it is important to get the car to a mechanic for diganoses.
If the light is not coming on when you turn on the ignition, check the bulb, it may be blown.
It could be bad with out turning the light on.
Yes, the check engine light is coming on for a reason. You need to take your vehicle into a service center.
Your oil compression is down probably... check the oil pan for rust and such.
check your oil level?
There are pages and pages of things that can cause a check engine light. You need to have it checked with a scantool. Then the code can be diagnosed and repaired.
'Well I have a 95 Buick LeSabre, and the check engine light keeps coming on. So I asked a guy at car-x, and he said that usually occurs when you go really slow on the interstate.'
The check engine light stays on when the computer detects an emissions related failure.
Slightly possible, not likely.
If it is a 1996 or later you can not.
It is not supposed to be on when engine is running unless there is a problem.