2000 Toyota Corolla p0171 help!!
Asked by Tommy May 13, 2023 at 06:44 PM about the 2000 Toyota Corolla CE
Question type: Maintenance & Repair
2000 Toyota Corolla, code p0171 when purchased.
Did fuel filter and line and nothing, cheap MAF from
Amazon and presto! Big increase in power and no
CEL. Three days later, same code, it goes on and
off intermittently but back to decreased power..
how could this be?
5 Answers
This code is telling us you have a lean air to fuel mixture. Too much air. Since the MAF is new, you want to look for vacuum leaks. Check your vacuum hoses for cracking and possibly a broken vacuum hose. Also check the exhaust system for leaks. If the exhaust system is leaking ahead of the upstream oxygen sensor fresh air can be pulled into the exhaust system and past the oxygen sensor. This can also trigger a lean trouble code. Hope that helps! Jim
If all the above checks good then it could be the cheap MAF sensor. I worked on a vehicle that the customer brought in his own mass air flow sensor to be put on so I did and cleared the codes then did the drive time protocol and the check engine light never came on so I gave it back to the guy. He drove for 4 days, then the light came back on, same code, so he bought another cheap one and brought it in and I swap it out cleared the code and started the drive time protocol but the light came back on within minutes, same code. So this time he let me run the diagnostics for the code and sure enough it was a bad mass air flow sensor. I convinced him to buy a factory mass air flow sensor and he whined a bit but did it, I put it on cleared the code and did the drive time protocol and no check engine light. Gave him back the vehicle, two weeks later he came back in and said it has never ran this good. He did keep coming back in for regular service after than.
First, this is a good reason to have a car checked by a mechanic before buying it. He'll find the problem and you can make the seller fix it before you buy it. One thing you should learn from the decades we've had cars with computer is that you never cheapen out on operational parts, like sensors. Buying OEM will save you a lot of time and headaches.
Thank you everyone for the help. I don’t know the most but know enough, how would I check for vacuum leaks?? Thank you!
The ideal way is use a smoke machine, but you can use water and just spray around the vacuum hoses and fittings, if the engine stumbles when you spray then there’s a vacuum leak.
