I have an 05 Toyota corolla, and have the check engine light on, I scanned it at autozone and error code is P0171 - System Too Lean (Bank 1). Which shows following possible causes: Faulty MAF, O2, fuel injectors blockage etc. On recommendation from the guy in autozone, I added fuel additive to clean the fuel line/ injectors. The check engine light went away for 9 months. But it is back on again. Tried putting in fuel additive again but the light remains on.