Hey Scotty. Big fan of your channel. I have a 2009 Nissan Maxima and recently I had a “ service engine soon” light on my dash. It bugs me because there is nothing else on my dash. So I went to autozone and plugged in the code reader to figure out what it was. The Code that popped up was P0171. System Too Lean Bank 1 & It also says replace Mass Air Flow Sensor. What does all this mean? Is it just one code with 2 problems( MAF Sensor & Sys Fuel Lean Bank 1) Or Just Replace The MAF. Please Let Me Know
P0171 code definition System Too Lean (Bank 1)
If you wanted to start firing the "parts cannon" at it then replacing the MAF sensor for a P0171 code might be a reasonable place to start IF you had a 4 cylinder engine. (a 4 cylinder only has 1 cylinder bank (Bank 1).
But I'm pretty sure all those Maximas are V6's.
(if I'm wrong about that then disregard the rest of this post)
So what is the P0171 code saying?
It's saying that the computer has "maxed out" its ability to adjust the injector pulse widths on Bank 1 to correct the air/fuel ratio to maintain a 14.7:1 mixture.
Typically this happens around LTFT (Long Term Fuel Trim): 25% and STFT (Short Term Fuel Trim): 12%. ((combined fuel percentage adjustment 37%))
So if this were a MAF sensor issue, why would it only be affecting Bank 1?
OR IS IT?
Maybe Bank 2 is showing high positive fuel trims but just below the criteria to trigger a P0174 System Too Lean (Bank 2) code.
IF that's the case, then replacing the MAF sensor may be a reasonable gamble.
Even if you don't do your own mechanical work, for a few dollars more than the price of a MAF sensor you can buy a scanner.
You could see what your MAF sensor is reporting at idle. (if you have a 3.5 L V6 engine then the MAF sensor should be reporting around 3.5 g/s)
You could see when the code is being thrown. If the lean condition exists on both cylinders. If the positive fuel trim(s) diminish at higher rpms.
You could watch a couple of videos on fuel trims just to familiarize yourself.
You don't need to be a mechanic to use a scanner. With all the information on the internet, (and youtubes) and the members on Scotty's forum, you have plenty of assistance to help you nail this down.
Check out Scotty's Garage on Amazon (Under "Diagnostic Tools"). He recommends the Ancel AD410 scanner as an inexpensive "good choice" ($46)
https://www.amazon.com/shop/scottykilmer?listId=2XW7WGTYW92WE
- It means you may need to clean/replace your maf sensor. Tons of things could cause a system to lean code tho. When the maf or oxygen sensors go bad, the car tends to run with to much or too little fuel, hence the lean/rich values. Rich is too much fuel and lean is too much air. you could have it properly diagnosed as a mechanic will see the data and know what's causing it, or you could try the maf sensor yourself and a YouTube video as long as it's not too expensive.
