Ok, after reviewing the previous charts a few times, I decided that the Mass Airflow Sensor and the second Oxygen sensor were not behaving the same when my check engine light would turn on. That is to say that I could follow the two graphs and they tended to behave the exact same way when everything was normal. When the problem would occur, my MAF sensor was indicating that the air intake was decreasing while the second oxygen sensor was indicating that oxygen was increasing. This suggested to me that the MAF was not reading the amount of air properly and so we were running lean, which caused an upward spike of available oxygen in the air.
I bought a reconditioned MAF sensor for about $80 + $50 core and replaced it on my car. It only takes about 5 minutes to do. I reset the computer and took it for a test drive. The performance seemed better at the time but it was hard to say because the computer had to readjust itself.
It has been about 220 miles and two week now since I replaced the sensor. The cars performance is good, it accelerates more smoothly and has more power. I haven’t put in a new tank of gas yet, so I have no idea if the gas mileage has improved.
So, if you have this problem and cleaning the MAF sensor doesn’t seem to work, that does not mean that the MAF isn’t the problem. Mine seemed to completely malfunction randomly and cause horrible performance. The gas mileage had dropped significantly even though the check engine light didn’t always turn on.
My car passed smog yesterday afternoon and was well under average for its class for all classes of pollution except CO. It could be that the catalytic converter is a little dirty and the CO reaction is slowed or that the engine is running a bit rich. The problem before was that I was running lean, so if it is running a little rich, it shows that the MAF sensor did fix the problem.
I also have a 2000 Corolla and I cannot figure out how to reset the “check” light. Would you please tell me how??
Try going to the Autozone or to Kragen/Parts America and see if they will rent you an ODB-II reader. They will charge you a $150 deposit that they give back to you when you return the tool.
The tool is relatively small and you plug it in to a connector in under your dashboard on your left hand side when you are in the driver’s seat. It’s about in the middle of my shin when I’m sitting down. Once you plug it in, you turn the key to the “on” position but don’t actually start the car. You will then have a chance to read the engine codes and clear them at that point.
Autozone will reset your check engine light for free if you ask them to. As for the p0171 code, my 2000 Toyota Corolla has the same problem and I’m in the middle of diagnosing the problem. Will know more later this week.
They will in some states but in California they are no longer allowed to do this. I think it is corporate policy. They are probably afraid they’ll get sued by someone if their engine gets ruined after having the light reset.
i have corrolla 2000 have a problem with check engine ligth i all ready changed plugs ignition coil cathalic converte both oxigen sensor mass air flow sensor and check engine ligth keep coming on can somnebody help with that
Have you checked the code to make sure its the same code? If it is running lean still then is it possible that you have one or more clogged injectors? You could try running a fuel system cleaner through if you haven’t already.