Reduced engine power?

Okay, so I know I have a few issues with my truck. I know I have an oil leak, but I just added oil to the truck a few days ago, my radio doesn't work, and a few other minor things. I was driving down the road and my reduced engine power light came on I smelled a weird smell and had absolutely no power, so I pulled into a parking spot. My car cranked and moved the next morning. Had a mechanic come out and look at it and his computer is not reading anything. However, my check engine light is on, and it has been for a few years. I had an fuel exhaust leak and had it fixed years ago but never cleared the code out. My mechanic doesn't know why it is not reading on his machine. Any information would be helpful.