My truck, a 2009 silverado with a 5.3 flex fuel motor, started showing p0171 a while back, but no one could tell me what it was. I had no loss of power or any other symptoms of the causes for this code. Well today I went to pick up some oil for a change and decided to let them scan it again. It came back with p0171, p0174, p0442, p0449 and p0521. I didn't have them clear it and proceeded with the oil change and also cleaned my maf sensor with the suggested spray. Immediately following, I returned to have another scan done. This time it's only reading p0174. I haf them clear it this time but the light was on again before i left the parking lot. Seems like I solved the other codes, but what would cause the p0171 to switch to both and now just p0174 without performing any repairs?