My check engine light comes on intermittently. Just had complete service done. Performed diagnostic as described in service manual. The operational code doesn’t come up, and already tried disconnection of battery to clear the obd-I
If it’ OBDI and a Ford, it can be intermittent. It will happen if there’s coolant temp issues that may or may not show up on the temp gauge (if equipped). They’re two different inputs on OBDI. One is a sender …the other a sensor.
Just so someone else may have more insight, how about a year/make/model/engine size …and “when” the light comes on. In stop and go traffic …etc…etc.
It’s a 1995 Chevy Tahoe, with 350 motor, 5.7 liter. The light comes on with no rhyme or reason.
I too recently went through several months fighting with my 1996 Tahoe with check engine light and rough running and failure to start. After several months of investigation and several sensors replaced and several thousands of dollars spent on probably unnecessary repairs, I discovered with the help of a good mechanic that one of the wires on the top crank sensor even though is showed good connectivity had the insulation melted off the wire due to the engine heat exhaust too close to the wire. The wire was covered by an aluminum shield and the wire would periodically short out on the aluminum fooling the engine computer into thinking something was wrong with the engine. Because the wire is inside this aluminum shielding it is hard to detect without removing it that this is really the problem. Several mechanics worked on it and replaced both the top and bottom sensors and several other things before we discovered the wiring problem.