failed emissions diagnostic codes read P0171 & P0174 I replaced both down stream O2 sensors but still same whats common?
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1999 Ford Taurus
Question: failed local emissions test
Answer #1mastertech6371 December 08, 2010, 16:55Master
not the o2 sensors. the long term trims are out of spec from a vaccuum leak, low fuel pressure or a bad mass air flow sensor. you already put in 2 parts it did not need, now get it checked for the exact issue then replace what the problem is. in other words, get the diag done and then fix it yourself.
ReplySparky1, December 08, 2010, 22:01Rookie
so where should I start? One guy told me it was the o2 sensors,but this didn't fix the issue. Running lean after replaceing the two rear sensors.
Answer #2DaveJHM December 08, 2010, 22:12Master
Roy's suggestions gave you some thoughts as to what could be the problem. And -- only a true diagnosis with proper test equipment can tell what is wrong for sure. You can replace gaskets, fuel pump, MAF sensor and spend a bunch of money and still not fix it. Get a good diagnosis and then if you choose you can repair it yourself and save some cash that way.