Code P0171 for 2001 Toyota Corolla

DRDEBS

MEMBER
TOYOTA COROLLA

Hey,
I have a 2001 Toyota Corolla 1.4 with 100,000 miles. I got this code, P0171 (I think) something or other was "lean." Anyway, I was advised to change the O2 sensor. So, when the light came on again after I had it changed I got the same code. SO, I had the other O2 sensor replaced. Honestly, I had no clue there were two of them when I had the first one replaced! Now the car runs terribly! What could be the problem? I would REALLY appreciate your advice! Thanks,
Dr. Debs

2 Replies

RASMATAZ

MECHANIC
75,992 POSTS

PO171 engine running lean can be caused by other than the O2 sensors.

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (Try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)