Check Engine Light? System Too Lean - Code P0171 or P0174 on Your Car or Truck

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Your check engine light is on, and you got the code P0171 or P0174, "system too lean." That means your vehicle's engine does not have enough fuel for the amount of air it is getting; a lean mixture. An engine running lean can have a negative impact on performance, and can cause damage! In this video, Andy walks you through the steps of diagnosing and resolving the different problems that could cause this code, from the simple: a loose intake fitting or hose; to the more complex: a faulty fuel injector or oxygen sensor.
Find your make and model in our playlists to see if we have a video on intakes, fuel injectors, or oxygen sensors for your specific vehicle:
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⚠ DISCLAIMER:
While 1A Auto strives to make the information provided in this video as accurate as possible, it makes no claims, promises, or guarantees about the accuracy, completeness or applicability of the content. No information contained in this video shall create any expressed or implied warranty or guarantee of any particular result. All do-it-yourself projects entail some risk. It is the sole responsibility of the viewer to assume this risk. 1A Auto is not responsible or liable for any loss damage (including, but not limited to, actual, consequential, or punitive), liability, claim, or any other injury or cause related to or resulting from any information posted in this video.

[@1AAuto]

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[@yevgeniymaksimovich8505]

Thanks for your advice! That was exactly what happened to my van after belt replacement. Fixed myself!

[@WaqarKhannyc]

Watch out for the A1 out they are scammers. They fucked up my car and they kept on sending a supplemental claim to my insurance every often. All when I've had a seizure attack and I was in the rehab. A1 AUTO YOU RUN SOUTH.

[@sickkat5910]

You're the only guy that starts at the beginning of the airflow and works it through that way. Everyone else starts at the 02 sensors and works back through electronically.... If the air isn't right going in at the first monitoring point, nothing is gonna come into alignment electronically. Thanks again for a clear, concise, orderly troubleshoot and repair!

[@jackierandall2230]

Check engine light was on so i lifted the hood and it was still there. Imagine that!!!

[@travism.3594]

Check engine came on for me 2 separate times years apart, dont remember the codes but light went off by itself a few days later. Now I'm a certified Mechinix

[@MB-df3tg]

😂😂😂

[@elizabethhartman3924]

Me too🤗😳

[@Meatwad.Baggins]

same here 😢 does anyone have a fix for this!?!

[@stevenbrown5210]

Good job that you checked that

[@zeezydoesit7416]

Wow!! This video just made my day. Opened the hood and realize the intake hose was loose and I tightened it back up and problem solved!! I can’t give this video enough likes

[@timj3277]

I haven't checked any of this on the car yet but I have to say that was very informative and gives me a really clear process to follow. Thank you!

[@jimbradley727]

It is an excellent video in relationship to these particular codes much more thorough than any I've seen and especially appreciate you referencing the front 02 sensors as a potential problem.

[@evanwilson9925]

This is so amazing! I've been a shade tree mechanic since I was a kid. I basically just learn everything as I go. In fact, I'd even so far as estimate the 30-% +/- of the money I spend on every project is on oopsies and lesson learn. But for vacuum leaks I've always had to pay someone to smoke test it for me. Using your method I just found it in 5 minutes!

[@Martin210670]

As usual, very instructive, clear, concise. Always check easy things first, that's my motto with any repair and you nailed it on my issue. As at the beginning of the clip, it was only the MAF that got loose at the air filter box. Put it back, cleared the code. Hopefully it was only that and nothing else comes up. Thanks for your precious help!

[@1AAuto]

+Martin Beaumont Thank you! We love empowering our customers and showing how to perform DIY auto repairs with our high-quality auto parts. 1aau.to/m/Shop-1AAuto-c

[@wandajekeqa5608]

Thank you for the run through possible issues regarding those codes. Very detailed and understandable. Great job, keep up the good work

[@levenge1]

Thank you @1AAuto , this assisted me in finding an intake leak after I had replaced the air filter causing both the P0171/0174 code as well as "Stabilatrak & Service Traction Control" errors on my 2007 Escalade.

[@17Shkurt2008Pavarsia]

I hope these tips help someone. Sometimes if it's not the vacuum lines or the mass air flow sensor it could also be a clogged fuel filter, fuel pump, injectors or the high fuel pressure regulator. If that doesn't fix the issue a corroded or a bad coolant temperature sensor can also trigger P0171 becausen it won't read the right temperature and it will mess with air and gas mixture by sending false information to engine's computer and that will lead the car to rough idles and throw P0171. In my case I cleaned the mass air flow sensor, I inspected the evap hoses for any leaks and I still kept getting P0171. Based on all the videos I've watched on KZbin not a single mechanic has mentioned the corroded coolant temperature sensor and that happened to be the problem on my 2005 MK4 VW Jetta 2.0L After changing the coolant temperature sensor the car worked fine and the code never came back.

[@badassbees3680]

Dude..thanks!!I guarantee that's my problem I never thought about em getting clogged since their pretty new.

[@uriahpierce3602]

thank you for making your videos straight forward clear and to the point, with out all the extra jargon.

[@PinBall3]

Also with Fuel Injectors the O-rings could be defective ( cracked or shrunk ) allowing a lean condition as well. Sometimes you can get away with spraying PB Blaster depending on the O-ring condition which will swell an O-ring and provide a temporary fix till you replace them. I did have that happen on a 4.0 Jeep ZJ but it showed as a misfire code.

[@cyrus138]

I sorted my P0171 by replacing the fuel filter after watching one of your videos. O2, maf, ignition, vacuum and exhaust system checked out.

[@tomvandentop3842]

1A Auto videos are a huge help and very professional, thank you! Started looking into my 2005 Rendezvous that had sat a while. First code was for the P0175 code to change the O2 sensor 1 bank 1.( I should've watched this video first.) Changed the sensor, cleared the code, good for a couple days. Then it threw a vacuum leak code, found a kinked vac line, so changed that. Today the P0171 code and found your video. Wish I could send a couple pics of what I found. Chipmunks built a nest in the airfilter box and also plugged the duct screen to the mass airflow sensor! Vermin!!!

[@richarddiaz591]

I had a P0174 code on a Dodge Dakota 2003, 3.9 V6, it was running rough and occasionally would throw other codes and backfire. After watching this video I went to work with the carb cleaner and noticed a leak between injectors 3 and 6, it turned out to be loose intake screws in the area, I retorqued and problem solved! Thank you.

[@dh1474]

Many thanks, great the way you take the viewer step by step through the possible faults.

[@MrPeterHaller]

1A auto you guys are the best all of your videos very comprehensive and easy to follow

[@blaketindle4703]

Excellent teaching! I’m glad I finally found this channel!

[@edilmendez9153]

Well explained voss!! You were born for this 👍🏻👍🏻

[@RedMeet12]

My 2006 2500 HD had a P0171 Code, I took the cover off the top of the engine, started the truck and immediately heard a leak from the drivers side hose connected from the engine plenum to the valve cover, thanks to this video, I found it pretty quick and fix the leaking hose.

[@enriquev8832]

Great video!!! Can’t wait to troubleshoot my car tomorrow morning! Thank you🙏

[@tammyyaniro5455]

I watched a lot of videos for this error code and yours was the most thorough and helpful, thank you!! :)

[@ronlee1949]

These were very good tips. I was ready to go by two oxygen sensors, but after watching this video and I checked all the lines and hoses I found one hose disconnected and I reconnected it solved my problem. Thank you very much.

[@FernandoGarcia-xr7zu]

What a revelation video, straight to the point, very clear with hands to work.

[@josephbowles4995]

Thanks again for the tips this Chanel saved me a lot of money god bless everyone

[@mikekeziah3064]

the carb cleaner trick found my leak !! thanks for the tip !!!!! glad I watched your video !

[@chriskaprys]

thank you for this. recently installed a new PCV on my crosstrek and got the p0171 after relearning the idle. Checked all the connections and air hoses .. lo and behold, when I reinstalled the rubber tube that runs down to the PCV flange, the tube cracked. I definitely would still be scratching my head if you hadn't given me the confidence to really inspect the air intake system thoroughly. Thanks!

[@sasusan1]

Super!!!. Your delivery is off the hook. Thanks man.

[@voradora]

Thanks for this video. It's just the right amount of technical, and saved me a lot of effort.

[@1AAuto]

+voradora Thanks for checking us out! 1aau.to/m/Shop-1AAuto-c

[@doschmitt1]

Your advice was excellent! Out of the 10 or so things that could have caused P0174, you suggested first checking every place where air could enter the system after the MAF. Sure enough the oil change guys had left a tube off the air filter box when they changed the filter. Popped it back on and what do you know! code gone. You saved me about $300 on a service call -- thanks for the common sense video.

[@christopherroncone6939]

Dude, you're the man!!! I had both codes on and a stupid hose was disconnected! I was about to go nuts.

[@jeffreyhildebrand4867]

Thank you for this video. Po174 came up on my 99 gmc the other day. I had just had a new rotor and distributor cap installed and your instruction lead me to a hose that the mechanic forgot to reconnect. I did and it’s running like a sewing machine.

[@ivancontreras7601]

Wow you are amazing! Thanks to you I save money and got rid of my headache, I found a loose hose/vaccim line.

[@charlestatakis9363]

Nicely done, a reasonable common sense approach and diagnosis.

[@dansweda712]

Great video! Right to the point and very helpful, thanks!!

[@samuelmedina5700]

Thanks Buddy, my engine light just went on, checked it with code reading PO171 system too lean. didn't know what the issue may have been, but you just solved my worries. you're Awesome. Thanks Again

[@NikeBoyMike15]

I just got the same code today, what did you do to fix? I tightened my air filter box and also had a hose like the one he shows disconnected going to see how it drives in the morning

[@Fishin4ReelTV]

Very helpful & detailed video. Walk through was very straight forward and easy to understand. Hopefully I will be able to fix my truck & get rid of those code. I’ll be back with an update soon!

[@bigbidness1457]

A man I my light been on for an minute I overlooked ur video after that. I seen no issue in so many other words Thankyou good day.

[@lawrencepellegrini2687]

Thanks for the heads up, replaced water pump and forgot to reconnect tube into air box creating a P0174, all good thank you

[@wllinc777]

yep you were a great help did a oil change and they left the hose unhook. Put it back and it wwas fixed. Thanks a lot

[@bereketgebregzabiher1446]

Excellent explanation.God bless you man.it helps a lot.thank you.

[@1AAuto]

+Bereket Gebregzabiher Thank you! We love empowering our customers and showing how to perform DIY auto repairs with our high-quality auto parts. 1AAuto.com

[@stephencannon3140]

Good starting point. The P0171 and P0174 are basically the same code. The difference in the number is another troubleshooting hint. 0171 USUALLY Bank 1. 0174 Bank 2. This is for V type engines. Consult Your factory service manual for the layout. Rear Whee Drive vehicles the banks are side of the vehicle and although should be standardized not necessarily so. The general layout for my RWD V6 for example Bank 1 is on the passenger side of the engine compartment looking forward from the drivers seat. ALwAYS check the layout, mine is 1-2-3 on the passenger side and 4-5-6 on the drivers side. Some might be 1-3-5 and 2-4-6....... DO NOT confuse cylinder layout with firing order. I just got a P0174 and cleared for now. When the weather gets better I will check in more detail but not panicking yet!

[@Gearhead68]

Thanks for this helpful video. I had the P0171 code on my 2019 Colorado, and found a loose hose on the intake. I reconnected the hose, started the engine, and the check engine light was off!

[@blobcsgo7190]

Thanks, got these same codes, and it was in fact a bad hose going from the valve cover to the top of the manifold on my chevy silverado 2007 4.8l Thanks!

[@madimakes]

yep was exactly my issue. 0:51. i must have jostled this while trying to get to the headlight. :facepalm: thank you! Thank you OBD reader and thank you 1A Auto Repair. fix was all of 2 minutes

[@cesareomiranda4485]

Really appreciate the good work from your tech's😁👍

[@fridaymwamba6637]

This is the most elaborate video on the subject that I have seen. So clear, detailed, comprehensive. I have a P2177 system too lean off idle bank 1. I have noticed passed 3 months that the vehicle doesn't start easily as it bid before. It now starts on third or fourth attempt. I am guessing it is more to do with fuel delivery than oxygen sensor.

[@1AAuto]

+Friday Mwamba Thanks for checking us out and the feedback! If you are having troubles getting this to crank over it sounds like possibly an issue with a fuel injector(s) or the fuel pump not working as it should (low pressure). Having this diagnosed is the best way to figure out exactly what is causing this rather than replacing one part and it being another. 1aauto.com

[@highviews4524]

Just checked my 2012 Honda Civic and found a 5/8" ID hose disconnected and reconnected it with the spring clamp. Hopefully that is enough. Great video!

[@jimtownsend7899]

Hey, that's my engine! The GMC 5.3L. I need to replace my purge valve this weekend to fix a P0440. And while I'm under the hood, I'll clean my MAF sensor and check all my connections.

[@Gr8nezz]

Very helpful, I had a couple loose vacuum hoses and the airbox not properly sealed.

[@BlackReapersClan]

Another Great video A1 Auto 👌🏾!

[@MarioGroleau]

Thank You! A hose leading to the snorkel was disconnected! I had Code P0171 and P0174

[@canyuto]

Thank you, your videos are great. In this case, I had a hose disconnected from the filter box, once attached I re checked and it was fine. Thanks again.

[@1AAuto]

+canyuto Thank you! We love empowering our customers and showing how to perform DIY auto repairs with our high-quality auto parts. 1aau.to/m/Shop-1AAuto-c

[@mahmoudmuwalla2397]

Good job you show the possibility of po171 but not mentioned how you finally fix the issue

[@col3life]

Thanks very helpful and nice touch at the end 😂! Any videos on P0300 with others like P0302, 4, 6?

[@nettosud]

Bro, super helpful. Excellent video.

[@darktoadone5068]

My 2013 Sierra 1500 just had a P0174 code, I can check all what you just covered over, I hope it doesn't end up being a lazy fuel pump. But I don't think it could because I can hear the pump engage when I turn the key on and the engines cranks up always on the first turn of the key, a fuel pressure check should indicate if it is though.

[@CoolAce1]

Incredibly detailed and helpful video.

[@1AAuto]

+Tree Garden Life Thanks for the feedback!

[@MegaMilagro1]

Excelente video thanks for sharing

[@gordhoenow6322]

That was an excellent video. Thank you.

[@charlesjackson7127]

Your Suggestions worked. Thanks!

[@crex7395]

MUST READ! I was going crazy trying to get that error code fixed. I have a 03 v6 4.2 and turns out the leak came from bolt bushings at passenger side intake lower portion. Ford released a service bulletin TSB 04-17-04. Hope this helps for anyone who struggled as much as I did.

[@foxmulder216]

Did you have to take the upper intake manifold off to put new bushings in? And do you have the plastic or aluminum manifold?

[@heathershark8895]

I got both of these codes. Im a single woman and appreciate you giving at least some advice for checking before I spend a lot of money with the mechanic. IT COULD BE A SIMPLE FIX!! 🙏🏼🤞I have fairh in God but not necessarily my abilities. He can guide me to the correct issue. Bless you!

[@sole_valley303]

I just wanted to let you know,thank you so much for the video u saved me so much money

[@1AAuto]

+Tony Vill Thank you! We love empowering our customers and showing how to perform DIY auto repairs with our high-quality auto parts. 1aau.to/m/Shop-1AAuto-c

[@atomicdmt8763]

excellent! very complete - THANKS

[@jeffalan6339]

It helps. I have P0171 and P0300, the 03 silverado runs very rough when near op temperature, black exhaust and spitting sound as well. Ah modern vehicles, I wonder if I can buy my old Nova SS back, simple reliable and durable. Today's stuff start it wonder when is something going to fail? Then what is it and caused the failure.

[@fixitfern5339]

Thanks for the very good information

[@donens9310]

Great video. Not covered, can a gas cap, vent problem cause a lean code as well? Since low fuel delivery would result in lean as well?

[@geradosaucedo1615]

Thank you for the video

[@ministervictorsimmons6014]

Thanks Sir this fixed my problem👍

[@rudytapia943]

Thank you, that was perfect, becouse my car is doing that, so now i know wat to do thank you, big help

[@fixit4182]

Very informative video thank you very much

[@20tea]

Just figured mine out! Replaced the injectors and intake manifold. After much headache chasing a vacuum leak, I found my new set of injectors were junk. Could be injectors as a cause of lean code or rich code. My case for lean was the injectors. Didn't want to redo tje intake manifold a 3rd time. Was worried I had a crack in the manifold.

[@Filioque_]

Thanks for narrowing it down to about 10 different things

[@alfredharrison597]

Listen for hissing or use carb cleaner and spay on some areas (hoses or where air flow would be, avoid electronics if possible) while engine is idling to see if the carb cleaner smooths out the idling, if no hiss or no change with idling and carb cleaner, check fuse for O2 sensor (usually under hood), if fuse is good, could still be a bad O2 sensor, if you want to try replacing the first upstream one whichever bank its on (cylinder 1 or cylinder 2 for the banks respectively) can try that route, as its usually cheapest. Harder down the line and more cost involved is fuel rail/fuel injectors, fuel filter and pump, EGR and PCM (Powertrain control module), good luck guys and dont burn yourselves on hot exhaust. Hot exhaust is best and easiest way to remove 02 sensor but its also the most dangerous, so keep that in mind and focus on safety.

[@ArtWAyala]

Thank you sir it was so well explained. Very helpful God bless 🙌

[@dennissecor8092]

Great video thank you for sharing!!!!

[@andrewcasares1413]

Love your videos man very informative

[@Joe-hu7di]

So my Subaru 08 3.6 has thrown this code. P0171 and P0174. I added some Seafoam to the gas tank on the parts store recommendation and it went away after resetting for a few weeks then came back. I have driven it a few weeks and it came back again. I have now done seafoam again but not reset the log. I checked all of the above pretty thoroughly and am considering the O2 sensors. But both codes at the same time doesn't seem reasonable since they are on different banks. If it were not for the lights on the dash I wouldn't think anything was wrong. Car drives great. 134,000 no oil leaks. They are over $100 a piece and I don't want to get it wrong.

[@GMC229]

Best mechanic 💪🏻

[@angelsaucedo2231]

thanks for the information👍

[@user-jb6hl5se8l]

Just put my transmission back in and am having this code. I noticed I have a small dent on my 02 sensor above the cat. Going to replace that and hope it fixes the issue

[@MarkAnderson-vg5vq]

Thank You, greatly appreciated your video

[@nostradamus4828]

Excellent explanations 👍

[@benhazeem7656]

Very informative video!

[@Thunder_Dome45]

Thanks. Mine has scared me twice in 2 years. But it still runs ok.

[@benbu911]

You sir should do more videos this through. Mad respect. Could you do one on the 99ish f250 super duty with the v10?

[@syfodias-jedimaster]

Very nice video may I ask is it possible for the mass air flow sensor to be dirty that could pause it?

[@syllylou77]

Thank you so much. Bless you.

[@fireboy5043]

Thanks Bro Great Info U the Man💯💯 Just solve my Problem🍾🍾🍾

[@emmettturner9452]

P0171 with intermittent Check Engine light on my 2000 Pontiac Montana with the GM 3400 SFI here. I found a rubber vacuum cap on the upper intake manifold that was turning into dust and mush. Sure enough, there was a pinhole of light visible through the cap. Just replaced it. Unfortunately, I also have a P0452 that’s likely from the replacement fuel the shop put in last year. It was making a high-pitched whine from the start and the shop refuses to warranty it just because it’s technically still working.

[@mark.r8900]

Great tutorial. My 2007 audi a4 giving a p0171. The car starts fine and idles around 1200 rpm then drops to 800 rpm and shakes. I unplugged the brake booster hose and the rpm stays same no change. Shouldn't the rpm rise because I am introducing more unmetered air? I am totally confused. Any help would be greatly appreciated. Thank you

[@unwillingduetolackofintere8999]

Thank u for that, very easy to, understand.

[@macguyver8698]

You just saved me 500$ thank you bro.

[@leobardorocha3081]

Exelent video brother...help me a lot....

[@southern_merican]

Very helpful 👍

[@cal48koho]

nicely explained. thanks

[@ananth218Canada]

your voice is so relaxing

[@allahonfingerprint3800]

Good information Thank you