Check Engine light/other

I have a 1995 xj6 with 112k miles. The check engine light came on while driving on a trip with approx 400 miles. It did this once before and went out after 3 months but this one has lasted 6 months. It runs the same, I check mileage which is the same, etc. Any idea what might casue this on longer trips?

Also looking for passenger headlight assembly and power antena mast.

thanks