P0171 code: recurring w/ increasing frequency

Question

P0171 code: changed m a f sensor: helped for awhile. Code sets w/ increasing frequency: was about every 1500 mi a year ago: now every 20 miles: drove less than 10k miles. HELP!

Answer 1

HI there,

There can be several causes for this code. Since you only have the code on one bank of the engine I would look for a bad O2 sensor on bank 1 or an intake manifold or some other type of vacuum leak. Sometimes the pcv valve hose will cause a small vacuum leak and the O2 sensor will see the lean condition.