Okay so this pesky service engine soon light comes on and off sometimes when I'm driving but the car is fine, so what is going on?

my they have a adaptor plug for your test

The car IS fine? 

or 

The car SEEMS fine (to you)? 

I suggest to interrogate the computer and find out about any stored fault code(s).

That light works on mileage since it was last told the oil had been changed. When you did your oil change did you reset it?  If you don't know how you'll find many guides on line.

Some expensive cars do have a means to analyse the oil and prompt you based on this.  For most, it's just a mileage counter.

You can jump the OBDI port with nothing but a paper clip (you just insert one end of the clip into one of the pins and the other end into another of the pins) and the check engine light will flash a pattern to indicate what code is set.  You can look up videos on how exactly to do it and what the codes mean, but an intermittent check engine light on an iron duke is usually caused by a failing oxygen sensor fwiw.  Good luck. 

Get a scanner and read for pending codes or history codes, that is codes that are about to stay ON.  A sensor could be bad or there is an electrical problem to the sensor.

The car has many sensors.  It is confused...because its shorts are in a knot..

. Try this.  Stop car. Shut off. Get out and go to gas filler cap and unscrew it off and screw it on again.  Get in car and restart.  I can do this while the light is red. And get back in and started before it turns green.  So it is quick.   That was after I drove my brand new car off the lot and drove 40 miles.  Then the light came on.  I did that once, and it fixed it.  I don't care where the issue was, it never showed again.  It has been "Years".  When my light comes on it is for an oil change interval time.(which is geared more to miles covered changes)  The other fluids I have to check myself at the same time to be sure everything is good.

Somethings not working right

Go to an Advance or an Auto Zone (or the like) & get them to read the code for free.  That's where you start. 

Take the car in for service.  It's possible the sensor is going bad, which is an easy fix.  Or you could have an intermittent problem that's setting off the sensor, and getting it checked now will save money down the road.

If the ashtrays are full Sell IT!