2002 F150 with the 4.2 - 6 cyl engine about 78K on the odo

Recently after filling up, I had the "service engine soon" light come on.
After reading this excellent forum, I thought since it happened right after getting gas, it very well could just be a loose gas cap. I took it off, put it on and the truck runs fine (always has).
I took it to auto zone and they read it as codes P0171 & 0174 - I had the codes cleared.
Sooo... my question is: If there is really a problem indicated by the codes, will they come back?

 

There may be a problem. Clean the MAF and see if it persists.

 

Those codes are lean for bank 1 and 2. Things to look for would be a vacuum leak or other problem behind the MAF. Best way to check for vacuum leak would be to start the engine and before it warms up spray behind and around the throttle body with carb cleaner. Because it happened right after a fill up I feel the need to ask was it empty enough for the low fuel light to come on? NEVER let it get that low because it can dredge up gunk from the bottom of the tank and cause the fuel pump to go out and that gunk will clog up the fuel filter. I would check the fuel filter while I was at it.

 

I think the low fuel light has only come on once since I bought the truck new.
But like I say, the truck runs fine, wouldn't it run crappy if there was really a problem?
Won't the codes come back if it was something more than the loose fuel cap?

 

It wouldn't necessarily run "crappy" with those codes. Clean the MAF and check for vacuum leaks and see if it comes back.

 

on this topic my truck has always had a P0171 bank 1 lean code just put a new motor in and still that code comes up.. any ideas?

 

Thanks for the input guys .... if it ever goes up to freezing outside, I'll clean that MAF rascal.
But still, no one has answered .... if you clear the codes (thinking there wasn't a real problem) will they come back on if there is?

 

Yes they will come back if triggered again.