P0171 - System To Lean (bank 1 )

[DavidSmith]

Hey Bill,

I recently have had the same problems with my 4Runner. My screws were stripped and my check engine light has not gone off after cleaning the MAF wires. I cleaned them twice with no luck. Did you ever resolve your problem?

Hi odb2guru;

thanks for your comments about the difference between the IAT and the air flow sensors. i took the MAFS off the vehicle and saw the IAT so i looked further.

i cleaned the air flow sensors and put everything back together. however, the screens that hold the MAFS in place were close to the head being stripped by a mechanic who hade taken this apart and clean it when i had it in the shop. (he apparently had cleaned the IAT instead of the air flow sensors because my check engine light came back on after i got it back from the shop.

i thought i might replace the screws. are the screws that hold the MAFS in place special screws? are they for sale by toyota or can i buy them anywhere?

thanks

bill

[oskerwize]

I also can confirm that the P0171 (system running too lean) code was caused by an accumulation of crud on the sensors. On my 2001 Corolla the air mass flow sensor is very easy to remove (2 screws) and is very easy to access. To clean the sensor I used brake cleaner which contains isopropanol, heptane and CO2 as propellant. This cleaner, although it's for brakes, doesn't leave any residue and does a fine job of removing the deposits.

In addition to the P0171 code, I noticed also that the car hesitated slightly on acceleration; that hesitation is now gone.

The air mass flow sensor as shown in the photos is probably the same for many Toyota models. These photos were posted on a Toyota 4x4 discussion forum, yet the same sensor is used in my Corolla.

Before cleaning:

After cleaning:

General view of Toyota air mass flow meter.

As I said, I didn't use contact cleaner, I used brake cleaner.

[oskerwize]

I got the famous P0171- bank 1 failure code and I had my MAF cleaned but no success. I cleaned my engine with Lucas injector cleaner and finally I will get P0100 -MAF failure code and after cleaning the MAF with CRC MAF cleaner and using Lucas deep cleaning I decided to replace my MAF. The engine started with no problems and then I had the engine light remove. After driving a couple of miles the next day I finally got the engine light turned on and I will check what the code will read. This is very frustrating. Can a vacuum leak cause this problem? I had o2 sensors and catalytic coverters change to no avail before. It ususally happens when I run the truck for long hours or long miles.

[shoki]

I have Toyota Corolla 2005. The check engine is on and it shows the P0171. I cleaned the MAF using CRC MAF cleaner spray but it didn't help. I reset the CEL but it came back after a day. i am wondering if reseting the CEL using Battery is different in removing code in comapre with reseting the CEL in Autozone!

[miniman123]

I had this problem with yaris when I worked at a Toyota dealer find it to faulty maf sensors hope this helps.

[shoki]

Thanks Miniman123! I think you are right, because after I cleaned the MAF, problem was solved and check engine was off but only for 2 days and CEL came on again. I think it takes a while for the computer to clean the error code becuase after 4 or 5 days CEL went off by itself!

[snagga1]

Just a bit of a tip for anyone who has the 2.7 engines-if you have an annoying check engine light coming up on and off at different times with P10171(lean bank 1) code(especially if it comes up while idling) then after extensive checking and looking at all the suspects(dirty Maf,leaking pipes,O2 sensor,dirty air cleaner,dirty fuel filter,faulty fuel pump, or leaking gaskets) and it still keeps coming up-in my case have found the real problem-Simply replace all your o-rings and rubbers on your injectors as they tend to shrink with age and heat and start to suck extra air into motor which the ecu sees with the O2 sensor output-straight away things start getting better and fuel economy improves as ecu doesn't have to try and make the trims richer to compensate for the extra air-this problem has even stumped a large number of Toyota service people -just thought I would pass it on😀