So the P0171 check engine code seems to be a rather popular code. I’ve searched the web quite a bit and most people who see the “Check Engine” light come on their Corolla have this code. It seems that this code usually comes up after the car has been driven 70,000-80,000 miles.
Common advice on the internet suggests that you clean the mass airflow sensor and see if that fixes the problem. The problem could also be caused by a faulty oxygen sensor or a vacuum leak. The corolla has two oxygen sensors. I haven’t looked to see where they are located but one is probably in the exhaust manifold and the other is after the catalytic converter.
So what is the cause of my P0171 error code? I don’t know. The ODB-II reader I used was one that is only capable of checking engine codes. I’m thinking about buying this reader because it should allow me to run the engine and actually look at the output of each of the sensors. I’ve tried listening for a vacuum leak but I don’t hear one. Of course, that doesn’t mean that one doesn’t exist. I just hope I don’t have to replace too many sensors, they are about $100 each.
My check engine light actually turned off after hitting a big bump in the road. This is the first time the light turned off w/o me having to clear it using a reader. I’m pretty sure it will turn back on though, it’s still not performing well in certain parts of the power curve.
I had ther same code for my toyota corolla 2001 I clean the MfS the problem disappear for weeks but after A long trip the code comes back. I think i have to change the oxinge sensor. I wish you luck>
I am having the same problem with a carolla that I have been working on. One other thing I was told to check is if any of the cylinders are misfiring. Not sure how much good that might do.
The problem might stem from a faulty gas cap. I was getting a light after the tank was down to about 1/4 and re-set after fill-up. Replacing the gas cap eliminated the problem. It seems that the vacuum spring in the caps goes bad after a while. It might be worth a try.
I am having the same problem with my 2000 corolla. I replaced the oxygen sensor in the exhaust manifold and it didnt help. I also cleaned the MAF sensor and that didnt help. I am not sure what the problem is.
First I changed the oxygen sensor and that wasn’t the problem. Then I used electronic cleaner to clean my MAF sensor. The sensor has a port with 2 little diodes, you must clean those. You may need a flashlight to see them. My car has been fixed for about a week now. While doing this, disconect the battery cable, to reset the computer. This worked for me, so good luck.