Check Engine Light, No Symptoms on Your Car? Diagnose Code P0171 Low Fuel Trim

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Have a check engine light but nothing feels different? Does your check engine code say P0171 Low Fuel Trim? Check out this video to see what could be the cause in your car or truck! In this video, Andy points out some of the common causes of the code p0171: leaks in the intake system that throw off the mass airflow sensor.
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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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[@SchrodingersBox]

Your videos are usually pretty good but you Totally dropped the ball on this one. The reason for a P0171 is because the oxygen sensor determines the combustion is lean and the fuel trim has to compensate over 25%. If this happens at idle then it would almost certainly be a vacuum leak after the MAF- particularly if the fuel trim returns to zero under load. However if the fuel trim increase is only under load- it is impossible for it to be a vacuum leak. Either a direct MAF, fuel pressure, compression pressure, or combustion inefficiency is present. Also there is never a reason to check the airbox on a lean code. Any issue must be AFTER the MAF sensor- never before it.

[@vicdgoldbrik]

Brother thank you. My light went on after my oil change. I went under my hood and yup those ding dongs forgot to tighten up my cover on my air filter. Thank you, you saved me about 1000 bucks.

[@leahbrum9971]

Awesome video! I got a code P0171 and P0125 The temperature is reading normal, heater works fine. It could be a lot of different things. Loss of power going up a steep grade. Put gas in car and the light goes on again. Service station is a dive and the gas was coming out so slow. Glad it's not the CAD though. Will have my son check mass flow thing you mentioned. Bonnie

[@muhammad-bin-american]

Exactly what I needed. No boring stuff. Straight to the point. My highly trusted 06 XB finally came up with this P0171 code and I was trying to figure out why. I did clean the MAF sensor and throttle body a while ago and may have messed up something. Thanks a lot!

[@DazBray87]

Just recently purchased a Insignia 1.8. Engine light came on then off, but now its back on - P0171 code showing on scanner. Going to try this before taking it to a mechanic. 👍

[@cliffordsutton-cv3vp]

Thank you sir, I cleaned my MAF sensor and found a hose I apparently knocked off when replacing air filter and plugs, will keep you updated as to whether this fixed the issue. Fingers crossed!!

[@5polarrex870]

Thank you so much for this, got the P0171 on my 09 Acura TL, checked around my air box and intake hose and wouldn't you know it there was a giant slit in the air intake hose (probably happened during last oil change), wrapped hole in electrical tape for time being and ordered part, $35 on Amazon, RockAuto didn't have it for some reason. Seen people say that it's a leak after the MAF, in my case, was the issue, The next 2 issues it could be is bad or clogged MAF or O2 sensor, 9 times out of 10 it's a leak though - unmetered air getting in.

[@syfodias-jedimaster]

Is it possible a o2 sensor could be faulty???

[@dvdr1985]

Thanks for the video!! I have same issue with my 2014 Mercedes c250. P0171 code came up but running like a champ. Noticed air box around filter was slightly ajar. Don’t see any other loose hoses. I tightened air box to see if this was the problem. should the check engine light go away on its own or do I have to erase the code?

[@jsoaps2]

2014 Chevy impala. Nothing wrong with performance just p0171 code. Checked everything no cracks in hoses, no hoses are unplugged, replaced o2 sensor already. Have no idea.

[@robertgoers6539]

Thanks for the heads up . Same problem with my car . My first car was a 1956 Ford with no sensors and much easier to work on . I only wish they were still made that way .

[@1AAuto]

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

[@user-tw1js5ye9s]

Ghtuy

[@atomicdmt8763]

might be loose/leaking OIL CAP and / or oil filler tube. I just found out!

[@Radiateprosperity]

My code reader says to check the PCV valve for cracks Etc the check engine light keeps coming on and off every so often so it happens to be an intermittent check engine light I'd appreciate comments regarding my issue thank you so much great videos

[@Rhonda858]

What could be the cause of a P0171 on a 2016 Jeep Patriot Latitude 2.0 we just replaced the MAP sensor but the vehicle still has a rough idle and the rpms run high while driving on the freeway approximately 65-70 mph the rpms are jumping up to 2200-2700 rpms. What could cause that? My husband already checked for vacuum leaks and says he can't find any obvious leaks. We just replaced the map sensor thinking that would fix it but it didn't so I'm thinking it could possibly be a bad Throttle Body w/Actuator IAC Idle Air Control or a TPS Position Sensor or even possibly a upstream 02 sensor. If anyone else can give me some advice on what I should fix next I would greatly appreciate it thank you!

[@eloymorgan8934]

That helped me bro! Thanks!

[@meanodustino9563]

Had this code happen on a lexus CT200h. Checked all hoses, Replaced a PCV it was sticky and as well as the MAF sensor but Not sure what it was but not those as the problem persisted and I stopped running down the rabbit hole. Gets frustrating sometimes

[@BryanG830]

P0171 and P0440 popped up at the same time. Car accelerating while at a complete stop. And does that also going uphill. It has trouble starting sometimes and sometimes when I start it and shuts off and then turns right back on. But no matter how easy it is to start it or how difficult it can be to start, it smells like gas so it has nothing to do with air or spark. It an fuel leak. I just don't know what it is or where it is. I need to find a video that's worth helping me. The gas gauge moves around too. And I replaced the fuel pump and fuel filter and the O2 sensors and the air filter and the spark plugs and the gas cap. Nothing seems to work. And there are no visible air leaks on no visible gas leaks. But it smells like fuel when trying to start the car. So it has to be leaking fuel somewhere. It's just not visible. The only thing I could think of is my car is trash. Little Chevy coupe with 240,000 miles. Jerks real hard between 40 and 55 miles per hour.

[@BulliKid]

Can you do one for running rich code

[@judyanngalanta134]

Very helpful!

[@monkey875]

1997 honda accord, 171 code after stalling on a puddle of water. Low Idle,up and down is minor still noticeable if you inside the car,

[@1AAuto]

+@monkey875 We wouldn't be able to diagnose an issue like that here, you may want to have a local mechanic take a look at it. Thanks for checking us out! 1aau.to/m/Shop-1AAuto-c

[@andymena3862]

Do I have to rotate engine to TDC before I smoke test the intake manifold? Or no need to,? Reason why I’m asking is because on this lexus 3,0 I’m getting smoke out of oil fill & oil dip stick.

[@blueryxfalls7949]

Nice and simple!

[@1AAuto]

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

[@AKB_48]

what was the hose that was loose hooked up too ?

[@michaelkemp9358]

Also my short term is between -1 to postive 2 on live data but my long term stays at 37 doesn’t move..so can anyone explain what that means and if it a fuel pump or fuel injector problem.. this all live data

[@TheGeezym23]

Thank you

[@1AAuto]

+Martin 876 kingston vlogs Thanks for checking us out! 1aau.to/m/Shop-1AAuto-c

[@michaelkemp9358]

Everything on my car has been change except the fuel injectors and fuel pump is that the only ones left that can be the problem

[@NaybaMade]

I have the p0171 fuel trim bank 1 code smh. I will check the hoses.

[@ZebraActual]

You should do a video on adding blinker fluid lol!

[@lseven9924]

Thanks I thought I had to replace a fuel pimp

[@taylor_4582]

Mine was a fuel pump

[@TITO0247]

I HAVE AN ACURA RL 2006, MY LIGHT ENGINE TURNED ON AND ON LETTERS ON MY DASH BOARD SAID (CHECK EMISSION SISTEM), THE MECHANIC WHO WORKS ON MY CAR SCANNED IT AND HAD THUS CODES (P0171 AND P0171) HE SAID IS THE OXIGEN SENSOR AND MAF SENSOR SO I SPEND $600 AND BUY IT 4 OXIGEN SENSOR AND MAF SENSOR NEW AND ORIGINAL, HE MOUNT IT AND ERASE CODES... AFTER 40 MINUTES IT START SHOW UP AGAIN ENGINE LIGHT ON AND SAID THE SAME AS BEFORE, (CHECK EMISSION SISTEM)... IM CRAZY WITH IT. THE CAR RUNS PERFECT, NO SHAKING MOTOR, THE TACOMETTER IS 750 AND I DONT FEEL ANY PROBLEM ECEPT SHECK ENGINE LIGHT WITH SHECK EMISSION SISTEM... WHAT ELSE CAN I DO SO I WONT TO SPEND MORE MONEY ON IT, ANY ADVICE PLEASE ?

[@HighTopMyers]

Hey 1A. Love your videos. I have a question: I broke one of the 10mm bolts when taking the intake off on my ‘05 Cadillac. I just wanna know if there’s a place I can buy just the bolts as opposed to an entire new intake manifold. Thanks for reading

[@carlosdart3118]

Nope

[@Mrfurballs]

my Silverado says P0171 system too lean

[@sergiomeza7046]

The grace and the peace be with you all from the lord your God our father, his son Jesus Christ, and the Holy Spirit, thank you! But how many of you know about the good news repent and believe in the gospel because the kingdom of heaven is at hand and crack your word the Bible and continue blessing you! Luke 6:20-28-35-40-42-44-46-47-48-49 10:25-27-37

[@dCash117]

My longft is at almost 40%, can anyone link a good video?

[@dCash117]

I'm pretty sure it's injector I can hear it ticking

[@rogeryanez8107]

I have this code however there is no vacuum leak, Is there anything else I can do or check? Thanks and love the videos ✌

[@1AAuto]

+Roger Yanez We wouldn't be able to diagnose an issue like that here, you may want to have a local mechanic take a look at it. Thanks for checking us out! 1aau.to/m/Shop-1AAuto-c

[@geoleiva46]

Hello good morning I have a question I replace my engine I have a 2014 dodge ram 5.7 don't start I have code u1477-00 p1b13 help me please

[@1AAuto]

+geoleiva46 We wouldn't be able to diagnose an issue like that here, you may want to have a local mechanic take a look at it. Thanks for checking us out! 1aau.to/m/Shop-1AAuto-c

[@Landaux]

I probably got one of the worst.. P0332 knock sensor

[@caza.mancos705]

Yeah😅👍🏻👍🏻👍🏻

[@user-tw1js5ye9s]

Ghthhhy