95 explorer check engine light on

I have a 95 explorer xlt 4x4 w. 114k miles. The check eng. light comes on sometimes when driving. If I shut off the engine and restart the truck the light is off for a hour or sometimes a day or so. I have the OBD 1 system and had the diagnostic check done on two diffent days, both times the check turns up w no error codes and all sensors are in range during the system check. The truck is running smooth no ruff idling or problems w. pick up. Can anyone help me with this problem.

It's hard to say for sure without a code. I do know that my 95 did the same thing, the code showed that the ECT sensor was--replaced it and no more problem.