Is 'Check Engine' Light a Trick?

courtesy of Bob, The Auto Answer Man

I have a question for you. I own a Nissan Sentra '97; it has 35K miles. Just recently (at 34,300) the service light - check engine - came up (while I was driving) and it would always be on. When I turn the ignition key, it comes up - even before I actually start the car, and when I do start the car it does not go off at the moment of start up as people tell me it should, because that's when computer supposedly checks the engine (is this true?).

So does it look like an electrical problem to you, or it's more serious? Is there a way to "reset" the computer so that to see if the service light still comes up? Or the only way to find out is to take it to the dealership to be checked on? The dealership charges $78 just for the diagnostics - seems like a lot of money to me. Thanks for your help and the great column you run.
Kess in Hayward, CA

Okay this is the deal. And I want everyone to pay attention to this because I will not answer this anymore. Anytime that light comes on, it means that the on board computer is receiving bad data from a sensor. Some people say, it only comes one to get you to go to the dealer to shut it off, or it comes on so you change the oil. Well, this may have been true in the past, but starting in '94 nope, sorry, you are wrong. Now, especially on '96 and newer cars, that light is an indicator that there is trouble and not someone "yanking" your chain as so many of you had put it. With some of the new inspection laws coming out... if you bring your car to an inspection and the check engine light is on, you will be immediately failed. In some states, they may require correction within 15 days or be subject to registration revocation. Not only will you be inconvenienced, but more likely that not, you are polluting my air! So do NOT ignore it, put black tape over it, pull the wires off the back... get it checked and fixed!
Good Luck!
Drive Safely!
Bob, The Auto Answer Man

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