uh my light keeps coming on

So since we got my duece to lay frame I now get a "service engine soon" warning only when I take it on the highway. No light driving around town.

Now, mechanically we did nothing to prompt this response, accept for changing the exhaust. I went to a expensive, tiny, high flow Cat, and a quiet flowmaster. I later stuffed a big glass pack between the two to quiet it down a bit. Now Lowboy might chime in on this cause Im a bit goofy on the exhaust sound...see you gotta have it just right...loud enough to sound tuff, but quiet enough you can converse. I think this is the fourth muffler combination I have had on it. I digress, the exhaust is new thats really the only thing we changed on it. Stupid light. We were careful to replace the exhaust after the o2 sensor.

Driving around town, it wont do it...only after driving for about 5 min, doing at least 65 will kick it on. sometimes it turns off when I slow...sometimes it doesnt turn off till i turn the truck off.

Any ideas?

you need to get it scaned and see what the code is it should be in histor

I had that same issue before and all it was , was one of the pins in the (for me the rear o2) was pushed out so somethings it worked sometimes it didnt. sooo IMO I would go under there and check all the plugs to make sure they are all secure.