Ford Repair: code: p0171, oxygen sensors, vacuum leak

Question
i have a 1997 ford expedition my check engine light is on. i had a diagnostic and the code p0171 apperce. i took it to two mecanics and they claim the fix it, but they didn't because the light is back on and the same code appearce. please help me!!!!!!!! whats is p0171 and what can i do to fix it?

Answer
Ivonne,

Code Po171 indicates a lean condition on cylinder bank #1 of the engine. On your Expedition this is the drivers side of the engine.  I don't know what your mechanics have already done, but I would suggest replacing both front oxygen sensors as a pair to start. An oxygen sensor has a life span of about 5 years and yours are now 9 years old if they are original. When they get older they are slow to respond to changes in the oxygen content of the exhaust and can trigger a code Po171.  If you continue to have the same code set after the replacement of both oxygen sensors then it is time to find out why your engine is running lean. Some of the most common causes are an ignition misfire and a vacuum leak.  I have also seen Fords EGR flow sensor (known by Ford as Delta Pressure Feedback sensor) to cause problems like that as well. A good mechanic with a scan tool can usually spot a problem like that in a few minutes.

I hope that helps you understand a little about what may be going on.