I put 60,000 miles on a Jeep with a check engine light. Also spent thousands on trying to fix it at various shops which would replace all sorts of things, to no effect, including about 5 attempts to replace a costly computer board.
Eventually had a redneck guy working out of the back of his pickup truck have a go at it. After hearing about the history he spent hours unplugging, cleaning, and replugging every single wire connection and socket. And the light stayed off.
