SES Light And Code P0171

[Halen5150]

Yesterday I filled the truck up with Exxon 89 octane. I had about a 2 hour drive ahead of me. About 20 minutes from my destination, the SES light came on and stayed on. Everything seemed fine otherwise. This morning I got Autozone to check the code. It showed P0171, which is Bank 1 too lean. I unscrewed the gascap and then screwed it back on. I started the truck up, and the SES light disappeared. I've searched through posts and from what I've gathered, it's most likely a leaky intake manifold gasket. It's an '00 5.3 with about 115K on the clock. The thing is though, I just had the truck at the dealership for $600 worth of maintenance a week ago. Any clues as to what it might be? I seriously doubt it was just the gascap...

[00Tahoe]

Just keep an eye on your codes as they appear. When my intake gasket started going, I got the PO300 code first (random misfire). Next came the PO171 and PO174 codes (bank 1 and 2 sensors too lean). I replaced one sensor and it did not fix the problem. The intake gasket is like $35. Set an afternoon aside with a buddy and you can have it fixed with no problem. Took me and a friend about 2 1/2 hours to do. Good luck.

[Butch 02 Denali]

Check your intake tube between the mafs and the throttle body too. A small leak there will act the same as an intake manifold leak.