I keep getting codes P0171 and P0455. on 2006 Chevrolet Equinox

I have replaced the gas cap numerous times. I have reset the code on two occasions, however it came back after about 200 to 400 miles. The vehicle has 70,000 miles and I am planning a tune up. I have noticed it is harder to start on many occasions.

Asked by for the 2006 Chevrolet Equinox
the 171 is a lean code. most common problem is vaccuum leak. the 455 is an evap code. stop erasing the codes so a tech can see the freeze frame data so he can see under what conditions the codes set.

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I was constantly getting P0171 as well which is a system to lean error. I thought it was the mass air flow sensor but it ended up being that the hose near the filter was rotting around the clamp and was loose. Dealership said it happens when the mechanic doesn't put the hose back properly after you get the oil filter changed with your oil changes. Hope that helps.