Have both codes 0171 and 0174 both systems 1 and 2 too lean banks 1 and 2. Car is a 2001 2.9l non turbo with 178K miles on it. original CAT converter and original sensors. Where do I start? I can replace the spark plugs, which were replaced about 25K miles ago. and I have a K&N air filter. Should I replace the spark plugs clean the K&N air filter and clean the MAF meter? does that make sense to start there?

What drives these codes to come up?

Thanks

 

I continue to chase this problem. I do have a K&N air filter that I cleaned. I also just took the MAF sensor out and cleaned it with a CRC MAF sensor spray cleaner. I did read that this could be a primary problem if the MAF sensor gets dirty from the K&N filter. Will report back on how this cleaning did. I cleared the codes and ran the car to reset the air fuel ratios. Will take several trips to see if the codes reappear.