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For the past....couple of years....my check engine light has been on and no matter what I do, it has stayed on. It may clear for a few hours, or a day, but always comes back. The code is P0174 or P0171 lean bank 1 or 2. I have replaced the following: All 3 O2 sensors, MAF sensor, Fuel pressure regulator, and the fuel filter.
Does anyone have any suggestions on what else it could be?
I Would Try The Idle Air Control Solenoid And/or Engine Coolant Temp Sensor. They Both Contribute To A Lean/rich Condition In The Fuel Regulation Sequence.
Thank you to everyone for the replies. The bad thing about just unplugging the light is that the problem doesn't go away and with the light registering as being on, it won't smog! You used to be able to disconnect the battery so the light would go off for a while to get smogged, but DMV has got hip to that so now they can catch that and you still fail!
I took it to someone and they indicated my O2 sensors are bad. I hope this is it but when the light went on for the first time in 2003, I replaced the top two O2 sensors, and just replaced the lower one. Do they go bad that fast??? I sure hope this is it.....
Don't forget to inspect the sensor wiring and connections.
O2 sensors should last for several years, probably on the order of 100,000 miles or better - however, there are exceptions.
Your problem could be an actual condition as opposed to a sensor failure - some casual thoughts are - serious injector fouling, major vacuum leak, blocked EGR flow.
Jamie I have a 1996 f150 inline with the exact problem. Did you ever resolve the "checklight on" problem after all o2 sensors and max air flow valve were changed. I have changed all items except the 3rd o2 sensor. I do not know where it is. I changed the 2 on the exhaust manifold.
Jamie I have a 1996 f150 inline with the exact problem. Did you ever resolve the "checklight on" problem after all o2 sensors and max air flow valve were changed. I have changed all items except the 3rd o2 sensor. I do not know where it is. I changed the 2 on the exhaust manifold.
Thanks,
mippps
Jesus christ glad to know I am not Alone!!
I have a 1996 F150 L6 2wd as well, and I have been battling the damn Check Engine Light for the past month.
I replaced all 3 O2 sensors, both pieces on the EVAP purge thing, and clean the Mass Airflow Sensors-god dang light is STILL comming on. I am running our of patience and Ideas. I will try to replace the Mass Airflow sensor next, well see if that does anything
Jamie I have a 1996 f150 inline with the exact problem. Did you ever resolve the "checklight on" problem after all o2 sensors and max air flow valve were changed. I have changed all items except the 3rd o2 sensor. I do not know where it is. I changed the 2 on the exhaust manifold.
Thanks,
mippps
The 3rd one is under the truck just behind the transmission. Its real easy to get at, youll see it.
Check Engine Light 1996 F150
The code is P0174 or P0171 lean bank 1 or 2. I have replaced the following: All 3 O2 sensors, MAF sensor, Fuel pressure regulator, and the fuel filter. 
Linear Mode
