P0171 System Too Lean bank 1 Chevy Trailblazer “Fixed with no parts”


All right, we got a chevy trailblazer here with a check engine light on and a stored code p0171 I got the G scan scan tool hooked up to it I’m just gonna scan the code real quick. I just want them to narak obd2 functions we’re gonna scan it for codes, and I’m going to show you in this video how to Diagnose a p0171 on the chevy trailblazer Typically what that means is there’s an engine vacuum leak or you could have a bad bad mass airflow sensor Or two sensor or there’s a number of different things, but typically P0171 means you have a vacuum leak Basically, it’s just saying that Bank one is running lean for one reason or another so way now. We’re going to Just verify the trouble code and then we’re going to look at the engine data and see if This engine is indeed Running lean I’ll show you how you can look at the fuel trim values and determine whether or not it is currently running lean Alright, so there. We go we got our p0171 system to lean bank 1 So let’s go back out over here and see if we can get I’ll go into engine data Data Let’s see if we can pull up our fuel trims That’s really all we need to diagnose this code is to look at the fuel trim baggies Typically a good field trim value is going to be right at zero you’re gonna Have a long term fuel trim and a short term fuel trim And as you can see here, I don’t have the right engine running yet bonus track here, but here It was a short term fuel trim bank one and our long term fuel trim bank one Let’s go ahead and fire this thing up and see where those are at Okay, so I actually had to change skin tools here because I was having a problem getting the data up on the generic scan tool so now I have the as a tech 2 hooked up to it and We’re looking at the fuel trim values here And as you can see the short term fuel trim is at 32% long-term at 24% Which means it’s adding a lot of fuel to compensate for lean condition Those numbers should be right around zero give or take you know maybe 5% at the most so what we’re going to do is go underneath the hood and hook the smoke machine up and See if we have any vacuum leaks that’s causing this thing to be running so lean I’m just gonna go right on the hood. I actually have all that stuff hooked up already so I can Show you guys What we found on this Trailblazer for vacuum leak? Okay, we’ve got the smoke machine all hooked up here We’re gonna smoke the intake manifold system for vacuum leaks as you can see the air fills I pulled out of this thing is nasty So it’s always gonna be a good idea to clean this mass airflow sensor if you find a dirty air filter like that You can just basically remove it Clean what’s a mass air flow sensor cleaner? I’ll leave a link in the video description below where you can get that mass airflow sensor cleaner It’s always a good idea to plug thing out and clean it In this case that’s not our problem, but I’m gonna clean that anyways I’m gonna put a new air filter in this thing But I’d pull it all apart to get the smoke machine hooked up And the best place do this is right through the air intake duct And you want to do it After the hour before the mass airflow sensor is just in cases there and take dump itself is leaking so As you can see we got a bunch of smoke there, and we’re sticking in here Mister just for some smoke down in through the intake system That’s gonna pressurize it and if there’s any leaks we’re gonna see smoke coming out And you can see right there We have smoke coming out of this tube, and this is just part of the air intake system. This is actually before the intake itself Chances are somebody probably had this Piece off the top of the engine and when they put it back down. They didn’t plug it in I’m just gonna plug it with my finger real quick to make sure we don’t have any other vacuum leaks This is the only leak we have that’s relatively easy fix, so I’m not seeing anything else We always have to pop that off and plug that back in we can verify it’s fixed Okay, we plug that breather hose back in on top of the valve cover and as you can see The short term fuel trim has gone negative Which is good that means? We’ve fixed a lean condition and basically what this is going to do Is over time that short term value is actually gonna bring this long-term value down Eventually those two are going to meet in the middle and this fuel trim is gonna. End up right at zero so that is Confirmed fix so with any generic obd, ii scan tool you can look at these fuel turn values and after you repair whatever the problem is you find whether it be a vacuum leak, or if you clean the mass airflow sensor or What whatever the case may be? as soon as you fix it you run the vehicle you can come back in and look at these fuel trim numbers and You’ll see they’ll start both will start getting closer to zero or it’s normally the short end will go negative and the long term will slowly Slowly equal out with the short term, and they’ll both end up around zero so this one here is definitely fixed We just plug that breather tube back in chances are somebody was probably servicing it and left that breather unplugged Pretty common problem if this video was helpful be sure to thumbs up button appreciate you guys watching subscribe to my channel Thanks Flat Rate Mechanic til next time You

37 thoughts on “P0171 System Too Lean bank 1 Chevy Trailblazer “Fixed with no parts”

  1. So most of the times when you get a lean code you have a vacuum leak? And those fuel trim figures on the tech 2 are at idle correct?

  2. Things I needed in this video. Smoke Diagnostic Machine https://amzn.to/2tbEMoe
    Mass air flow sensor cleaner: https://amzn.to/2HbyNJm
    Air filter and tune up kit: https://amzn.to/2vt1pbA

    The one tool every mechanic should have: http://amzn.to/2FN2r70

  3. What were the LTFT on bank 2 ??…if the LTFT were say 22% the DTC for bank 2 (01074) it would not set a DTC…that would make me change direction as far as troubleshooting…."bank specific" vs. a leak that would set both DTC's….a leaking intake runner on 1 bank vs. a leaking MAF sensor bellows !!

  4. Flat Rate, what would it mean if the long and short term readings are opposite of the reading you got in this video? I have a 03 tacoma 3.4l with the p0171 code and my fuel trim readings at idle were 1.6 on short and -14.9 on the long. Cleaned MAF and checked for leaks by spraying card cleaner around intake and vac hoses. No change in engine rpm. I suspect weak fuel pump or clogged/bad injectors?

  5. I got this code on a 2000 ford 5.4l I I could erase the code and it would drive ok. It turned out to be a unplugged fuel injector

  6. Hello I have a Toyota Corolla 2000 which is the same problem ( po171 and po302) , what should I do ? Change the intake manifold seal ? or change the spark plug cable for it ? Thanks for your video. It's pretty awesome. I have learnt something else more about it.

  7. Please HELP me out , its been 2 weeks and no mechanic can fix my car.
    I am getting code P0171, i have checked all leaks , the shorterm fuel trim is 46.88% , long term fuel trim 18.45%.
    Air fuel ratio 26.75 , O2S1 -3.5mA, O2S2 is 0.9V ,

  8. I have the same code on our 2003 Chevy venture mini van , the intake manifold gasket was replaced 3 months ago . Dam that engine compartment is tight " 10 pounds of shit in a 2 pound bag " to look for vacuum leaks .

  9. Thanks for the video brother my 2001 yukon xl is doing same thing. Conveniently a day after valvoline did my oil change??? Im thinking they did something similar , hopefully its as easy or close to it to fix. Only thing is i had a 02 heater code pop up after the initial lein code?.first it was bank one sensor one, cleared it. Then it was bank 1 AND 2 lein. Cleared it. Then it hit me with a bank one sensor 1 heater switch?? If u get around to this comment, what do u think?

  10. I got the same thing my 2012 Colorado. I did the throttle body clean. When I drove the truck the next day the idle idle up it took a while for it to idle down and then on the end of the day that's when the check engine light came on I put my code reader on it and it read p0171
    Where should I look for the air leak?

  11. Could the vacuum leak be in the vent/heater/defrost under the dash, mine pops when the vehicle is off or starting up.

  12. The Chevy LS1 V8 engine in my Holden Commodore which started throwing it today,the catalytic converter has been rattling since last week ever since I was driving my morbidly obese sister home from university & the cat hit a speed bump in the supermarket car park on the way home.

    Being an Australian car,it is right hand drive so a P0171 happens on the passenger side over here.

    I know that fitting 100 cell cats or doing a cat delete will set codes off in an LS1 powered car which hasn't been tuned,so I want to order a new set of headers & 200 cell cats & a brand new cat back exhaust system to replace the old one.

    My point is that the P0171 appeared after the catalytic converter got whacked !

  13. After you fix the problem with the code automatically go away or do you have to drive the car a certain amount of miles for it to clear itself.

    I have that lean code and i notices my air intake duct hose was torn so I replaced it with a new one but I still have a “service engine soon” on my dash. I’ve driven the car about 3-4 miles since replacing it

  14. My car Nissan versa 2015 had same problem. Now when start to drive it hardly moves and not go more than 20 mph

  15. Nice Video but Fuel Trim right at zero is a big statement LOL never seen on at 0 before. Just cutting up!

  16. Hello, its this data corect?
    I have random the light check engine on and the P0171 error.

    The car is chevy aveo 2010.
    https://youtu.be/Qph5mtIwxJM

  17. Hi, I get this code only when I idle for too long, maybe at a drive thru that's taking too long. I get the code and then after a while, sometimes the next day, it disappears. I cleaned the MAF and changed the air filter like you did in the video. Just wondering if it keeps happening it would damage the engine. Ford F-150 2008 4.6.

  18. 08 Envoy 4.2, same code. I watched this video and I checked that same hose and guess what, that same hose was hanging off lol. Same problem. I just bought vehcile so previous owner left it undone…. I saved money as well, which is the best part!!!!!!!!!!

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