1992 Chevy Silverado V8 Two Wheel Drive Automatic 148000 miles
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When I'm driving, about 5-10 minutes, the engine light comes on. The guy I bought it off of said he took it to a shop nearby and had the code reader check it out. The guy who ran the code reader found nothing wrong with it. In other words the code reader didn't say anything. Why does this happen. And what could be some possible reasons it comes on.

Also after about a 30 minute drive after I park it, it gives off a bad smell. But I'm not sure what it is.