P0171 and P0174

Coolwolf1015 · May 13, 2026

Ok, I have a 2005 Chevy Silverado 1500 5.3 and I am getting these codes. I’ve done a little bit of research and I just need some ideas on what I should check first. The truck has already had the intake gaskets replaced and they are brand new. I should also add that the truck drives normally and just has the light on. Another thing to add is that when looking at the scanner, bank 1s fuel trim is 15.6 at idle and bank 2 is 13.3. When the truck is revved up to 2500 rpm and sitting there the trims lower down to 10 or 11 as well. That’s still high in my opinion and just want to know what I should check. The MAF on the truck has also already been replaced. If anyone has any ideas what I should look for or what I should check next that would be greatly appreciated.

stutaeng · May 13, 2026

When you have both bank lean and the numbers are close, you can suspect fuel delivery, so check fuel pressure...

To see if you have a vacuum leak, you monitor fuel trims at idle, then rev tbe engine and the fuel trims should improve. Yours did at 2500 somewhat. Can you check and rev a bit higher?

You may have a combination ofbthings going on also.

Marky Dissod · May 14, 2026

May need to check the intake manifold for OTHER leaks. It has several auxiliary fittings on it that may test well under pressure, but fail under vacuum,
and every atmospheric intake manifold operates under vacuum.
Also may want to recheck installation & tightening of various intake fittings, anything loose between MAF and O2 sensors should be leak free.

ORVietVet · May 15, 2026

Was the air tube/snout inspected for leaks?

CPB · May 15, 2026

Marky Dissod said:
May need to check the intake manifold for OTHER leaks. It has several auxiliary fittings on it that may test well under pressure, but fail under vacuum,
and every atmospheric intake manifold operates under vacuum.
Also may want to recheck installation & tightening of various intake fittings, anything loose between MAF and O2 sensors should be leak free.

I'm a monster and just spray TB cleaner all over the fittings and intake to locate leaks.