Scotty,I got the error code P0171 on my daughter's 2006 Toyota Corolla S. Hooked up my Blu driver and saw the LTFT ranged from +12 to +39 at times. I replaced the Intake manifold gasket,cleaned the mass air flow sensor,replaced both 02 sensors and replaced the spark plugs and air filter. The MAF is reading normal,but the LTFT stays between +8 to +15. The STFT seems normal close to zero. The car seems to drive normal, what else can I do to get the LTFT down,or should I just chalk it up to age of vehicle, has a 155,000 miles on it. Thanks for any advice.
What does P0171 represent? (check on obd-codes.com if you don't know)
The engine is trying to add tons of fuel because it thinks the mixture is lean.
This is often caused by a vacuum leak, or faulty injectors. What is your MAF reading at idle?
MAF at idle is around 2 to 2.5 grams per second.
how do the oxygen sensor charts look?
Might be a dumb question, but are you asking the voltage of the sensors?Just replaced with Denso sensors,so I haven't really been checking the voltage.
yes the voltage waveform
Sensor 2 .035 to .7 wave up and down. Sensor 1 2.9 to 3.6 and fairly steady. Like I said both were just replaced.
Here is what a Toyota parts center and engine code sites have to say (quoted info links provided):
Troubleshooting P0171 Code
Oftentimes, a P0171 means that your Toyota is having trouble with a dirty or faulty mass air flow (MAF) sensor, or a vacuum leak downstream of the MAF sensor (perhaps in the PCV line or in the valve itself). Of course, this code can also signify a bad O2 sensor in bank 1.
Additionally, it's rare (but still possible) that a P0171 code can be tripped by a plugged fuel injector, by a dirty fuel filter causing low fuel pressure, or even an exhaust leak before the first O2 sensor€¦isn't engine trouble code diagnosis fun?
- Most of the time, the best way to respond to a P017 is to try cleaning the MAF sensor and the lines running to and from it. This will often resolve this issue.
- When you clean the MAF sensor, be sure to inspect all of the lines including the vacuum and PCV hoses. Look for kinks, cracks, etc. and replace the lines as needed. Additionally, be sure to check all of the connections and hoses on the air intake and check for intake manifold leaks.
- Finally, it's never a bad idea to change your air and fuel filter, especially if they're just about due for replacement anyways.
Additionally...
P0171 TOYOTA Possible Causes
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection
Tech Notes
If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replace the air filter and clean the airflow meter. If the problem persists the front oxygen (O2) sensor may need to be replaced.
Links:
https://www.engine-codes.com/p0171_toyota.html
Also a bulletin was also made for your car check it out, apparently its so common and simple you should be able to get it done for $200 or so:
http://toyota-solutions.blogspot.com/2011/02/got-p0171-blues-in-your-toyota-corolla.html
