My son has a 1997 Ford Taurus. We cannot get the check engine light to turn on when the key is first turned on, therefore he cannot get it to pass inspection. Every year we think it will stay on durin

We cannot get the check engine light to turn on when the key is first turned on, therefore he cannot get it to pass inspection. Every year we think it will stay on during start up, but it stays off.  Even when the mechanic hooks a cable up to the connector under the dash and reads codes, the "check engine soon" light is off.

Two years ago, we removed the entire dash board to replace the bulb, but when we touched it to remove it, it turned on.  It worked for a few months, but then at the next inspection it would not light up again.  The mechanic could not get it on.  Then a mechanic who know '97 Taurus cars well, did a simple thing under the dash and the light came on.  This year we have the problem again.