CODES P0171-P0174

MY GIRL IS SICK!
This morning when I pulled out on Hwy 2 lights came on Traction Control and Check Engine and wouldn't get over 2000 RPM...
I get to work and scanned an 2 codes , P0171 and P0174 ... would you say replacing MAF sensor would fix my problem..

 

both banks lean. Look for a bigger vacuum leak. PCV / Vacuum booster line. doubt its the maf

 

P0171 can be a bad/dirty MAF sensor, but in most cases it's usually due to a vacuum leak somewhere (dealt with this code myself awhile back and that's what the shop said). Less likely culprit could be a bad O2 and/or air/fuel sensor or possibly an exhaust leak.

I think P0174 is the same kind of code but for bank 2 instead of bank 1 like P0171 is for, so my bet is on a bigger vacuum leak

 

Sounds like you have a vacuum leak, dirty MAF, or dual exhaust leaks. Check all connections post MAF, intake and vacuum hoses. See if you find anything obvious.

 

ok will check... thank you.

 

Couldn't hurt to clean the MAF sensor too while you're at it, it's very easy to do. Use MAF cleaner only, not carb cleaner or generic electrical cleaner.

 

Hello Everyone, I know this is an old thread and I'm not sure if I'll get a reply but it's worth a shot I guess. I have a PO171 & PO174 code on my 2015 Toyota Tacoma (4.0 V-6). I've replaced the MAF, had the engine tested for pressure (which showed to be all good), and filled the system with smoke as to find any potential vacuum leaks. I didn't find any leaks in the system and the replacing the MAF didn't do anything. I also tested the ignition coils (no issue found), cleaned the throttle body, and fuel injectors which seemed to help for a few miles but then the truck went back to driving sluggish. It seems like my Tacoma drives great at certain times but other times will shake as if it's about to shut off similarly as if a vehicle is running out of fuel. The mechanic who tested the fuel pressure for me said it couldn't be the fuel pump because the engine pressure was good. I'd also like to mention I had additional codes which may have relation to the ones mentioned: 01604 Startability Malfunction, P1605 Rough Idling, P219A Bank 1 air-fuel ratio imbalance.

From reading everyone's comments it seems like a possible solution is replacing the fuel rails, replacing the fuel pressure regulator, and eventually the screen filter/ Fuel pump.

Pls help.

 

You really need a fuel pressure gauge on it when it's running bad to truly rule out a fuel pressure problem, pressure regulator and filter are part of the pump assembly, the rails are just hollow tubes that hold the injectors I don't see how they could go bad.

 

There is also a fuel pressure regulator on the fuel rail.

 

Oh ok I was thinking these were return-less fuel systems.

 

For others to understand:

 

My 2010 Tacoma Prerunner 4.0L has had the P0171 & P0174 code problem for a while now. I have replaced the maf sensor, fuel pump, a/f sensor & the oxygen sensor. Went to have the codes cleared only to find out that the codes are marked as permanent now. Of coarse I shouldn't have started shotgunning parts at what all I thought was the issue. There also doesn't seem to be a vacuum leak, so I'm close to throwing my arms up & just deal with the cel always on!

 

Could also be bad fuel... ive had a few with E85 that caused a lean code

 

How do you know there isn't a vacuum leak? Have you looked at fuel trims while driving?

 

I need to take it to an actual mechanic so they can actually look at fuel trims. I say it "doesn't seem" to be a vacuum leak only because we've hooked up the smoke machine to it and also sprayed carb cleaner while engine is running to see if the rpms would go up or down with no luck.

 

it looks like these codes could have more than one root cause. This youtube video https://www.youtube.com/watch?v=8G4iG6JgpUE can show you all the possible causes. Mine (2011 V6 4.0 Tacoma) has this code since a year ago. I just plug a scanner to read the fuel trims and whenever accelerating the long FT in both banks go above 30% while the shorts stay below 10%. I also notice a smell on the exhaust when this code first appear. last month i just run a smoke test to the intake system and found nothing. I don't have loss of power when accelerating but will do a gas pressure test and all related diagnosis to this fault!

 

Great post! Have you noticed a decrease in your fuel economy? Seems like ever since these 2 codes became part of my daily life, what use to take me a 1/4 tank of gas to get to work now takes me a few notches over a 1/4 tank of gas.

 

Sure, mine will usually give me like 6km/l and now it’s around 5. The thing is that to get rid of this code, there are so many possible causes. I started to get a 25USD scanner and start to learn how the whole combustion and sensor system should be running… not something that is going to happen soon.
Take a look on this https://www.autoserviceprofessional...-how-it-works-and-how-to-make-it-work-for-you

 

Actually just ordered an obd2 scanner from AP for $20, that's also supposed to be able to give you live data of your fuel trim levels. Next step would be to just remove the cel led chip, considering that I'm already about to change the instrument cluster gauge led chips to a different color.

 

Finally, no more p0171 & p0174 codes! After months of shotgunning parts at this issue & searching for vacuum leaks, I finally found the issue & fixed it. For me, the problem was the upper intake gasket.