Frankzao

I have a friend who has a 2001 MAzda Tribute. It just recently began to give him problems. No CEL code at all. He took it to a mechanic and they changed the emergency (accident) fuel stop switch and it worked for a couple of days and now it stopped again. When he put it on the computer the car shows that it has gas and spark and that everything is ok. But still it does not run. at this point the Mechanic says take it to the dealer. Any ideas?

Does code P0431 really mean this: I got one. I cleared it and it has not returned. Any thoughts?