If you have an OBDII port, which for most vehicles became standard in 1995, you can just attach a scanner and see what it pulls. It will give the fault code(s), next google that code along with the chassis your MH is built on and it will tell you the fault. Depending on what it is, you can just clear it -- if the light goes off you know there is an issue. Vehicles can throw codes for lots or reason and CEL will come on, often for the smallest things these days.
You mention SMOG, it could be as simple as the fuel tank cap wasn't tight enough while running the engine causing a vacume pressue issue and that can set off the CEL. I once got a CEL for a engine missfire while towing heavy up a hill in my former TV. Used the scanguage to find the code, cleared it, knowning if the problem occured again it would re-light the CEL and I would address it. Never occured again, and clearing the code myself saved me a trip to the mechanic and a diagnostic charge -- not to mention kept us on the camping trip.
Of course if the google search reveals the code is major item, time head to a shop.
FYI I use ScanGuage II for monitoring and reading the occasional code. There are all kids of readers and all kids of prices, and auto parts shop can help -- may even let you borrow/rent scanner.
2007 Chevy Duramax LMM/Allison
2012 Jay Flight 29QBH
2012 Jay Flight 26BH (Sold)