P0171 Trouble Code: System Too Lean Bank 1 Diagnosis

[Music] all right we got a toy over here it's got a check engine light yeah yeah don't tell Scotty let's check it out - we got now normally I'd use the auto LMS 9:06 to look at codes and help me diagnose things today we're gonna use this auto tell al three one nine see if this thing can help us diagnose this vehicle all right first thing we'll do we'll hook up this little code reader and scan for codes see what we got going on in general your DLC or data link connector will be somewhere under the dash on the driver's side right here at most vehicles that's where obd says it's supposed to be located and right here we'll go ahead and hook it up all right now that usually will power up your your a scan tool or in this case code reader just by plugging it in but we need to turn on the key before we're gonna read anything all right we're just gonna take the key and then turn it on but we're not gonna start the vehicle we're just gonna turn it on so we can talk to this engine computer all right as you can see it's a bit crude we only have three buttons right here so I'll keep you focused right there so that way you can see what I'm doing right now we're just gonna hit enter and let it try to see what protocol this vehicle is using all right there we go first thing we can do is read codes so we're good and click that read codes we got stored pending and previous and we'll just go with what's stored and we got a p0 171 system to lean bank one that is a four-cylinder engine so there's only one bank but we got a lien that lien code here all right now that you see a p0 171 system to lien what does that mean basically in quick terms it just means we have an heir or a fuel problem in order for a vehicle to run it wants 14.7 parts of air per one part of fuel so in this case we either don't have enough fuel getting up into the engine or we have too much air getting into the engine and it's throwing off that air fuel mixture so let's check some more things out so we can find now we would like some direction which way to go do we want to turn right or do we want to turn left or do we want to go straight ahead that's kind of where we're at right now and so one of the ways that can help us decide which direction we're going to go is to view the fuse front if I could say all right we're gonna view the freeze-frame right there and basically what obd2 is required to do is when the check engine light sets it takes a snapshot of all the operating parameters and so we'll go take a look at that and see what it's going to tell us all right let's see what this tells us what was going on when this p0 171 set all right we were in closed loop so that means the vehicle was using oxygen sensors to tell it what air fuel ratio to use that's a good clue let's see our load on the vehicle was ten point six percent which is not much the next one down is our coolant temperature sensor and we were at 185 that's a good data pid' to look at that tells us the vehicle was fully warmed up so we don't have to worry about trying to find this problem on a cold engine so that's a good clue the next to data pits that's going to be our short term fuel trim and our long term fuel trim and you can see right there thirty nine point eight and nineteen point five that's huge those are huge numbers what is that about sixty percent almost 59 percent so there that was definitely a lean condition the computer was having to add almost sixty percent more fuel to get this vehicle to run correctly let's see at our rpms 696 so the RPMs were right where they're supposed to be this vehicle should idle between 650 and 750 so 700 is perfect you can see that we weren't moving so it was at sitting still so that's a good clue this is an idle problem right here we weren't moving and our our rpms were at idle our intake tare and air temperature was at 84 degrees and that's it that's all we got but those are some excellent clues we can see that basically this set on a warm engine we had high fuel trims and we're at an idle not moving so those are excellent excellent clues to give us direction alright one more thing I want to look at while I have the tea on and the engine off it's going to live data I want to see the mass airflow grams per second I want to see it in the point four two point five range I don't want to see anything ridiculous let's see now in this little hotel I have to change the unit of measure to metric so I can see that in g/s and we'll just scroll down see were ya there we got mass airflow grams per second 0.5 so we want to see 0.4 0.5 right in that range on most of these Toyota's and so we're looking good right there what we don't want to see is like a 0 or 200 or 45 grams per second or just something weird like that where we know with the engine off we shouldn't be seeing very much air movement at all and so that that grams per second means we don't have much air movement at all so we're in the correct range right there so that's not going to throw our sensors and computer off because basically we want to narrow down do we have a problem with the fuel getting from the fuel pump into the engine do we have a problem with one of the sensors like a mass airflow or an air fuel ratio sensor or do we have a problem with too much air getting into the engine like pirate air that's unmeasured and when we're dealing with the high fuel trims at an idle that's usually an indication of a vacuum leak or pirate air after the mass airflow sensor so let's go check under the engine and see what we can look at now we'd like to narrow this issue down is it the problem with the fuel pump getting fuel up here to the fuel injectors is it a problem with the fuel injectors or maybe the the fuel filter down there is it plugged and so it's not allowing enough fuel in there do we have a problem with a vacuum leak sucking too much engine are sucking too much air into the engine do we have a problem with our sensors like our mass airflow sensor our air fuel ratio sensor that's down there so that's kind of we want to see which way to go and for me as it just as a general practice I like to do as much looking around as I can before I start the engine and so one of the best ways to do that is do an actual visual inspection so let's do a visual inspection of the engine area and we'll start with the mass airflow sensor which is over here it's only two screws in a connector so we can easily pop that out make sure we don't have something caught inside there skewing our results alright as you can see here's our mass airflow sensor only like 10 seconds to pop out so it's easy to do a quick visual inspection and so right here these little elements right here that's your intake air temperature sensor we're not concerned with that right now it looked like it was reporting just fine and right here those two elements right there one is your mass airflow actual heating element and then the other one is a little temperature sensor in there to keep that heating element at a certain degree but basically we want to look at that and make sure we don't have a bunch of garbage in there hair dirt anything trapped in there this one looks nice and clean I don't see any issues with that in there so I don't see anything just with a quick visual inspection that's gonna stop this airflow sensor from working now if it was dirty and I needed to clean it I would just use some mass airflow cleaner right here I would just spray it in let this stuff fall out try not to get try not to hold it upside down and spray it where stuff is gonna go inside where all the you know transistors and things are we're gonna spray like that let it drain out and we're gonna let this thing sit until it gets good and dry we do not want to plug this thing in and energize it while still wet because then you'll be buying a new airflow sensor all right as you can see I have the mass air flow back installed and if you didn't know what it does basically it measures the air that's coming in through this intake tube and it's converting that to a grams per second sending it to the computer the computer is using that to calculate how much air is actually entering the engine so as you can see as long as the air that it's sensing right here is the same amount that's going into the engine then we're a ok but what if we have a problem after that where air is entering this airflow sensor is not going to see it so our next visual inspection we want to look and see if we can find if there's any pirate air going into that that's not being sensed by this airflow sensor and I'll be honest with you when I see high fuel trims set a check engine code at idle the first thing I suspect is pirate air that we have a vacuum leak or air entering the engine that's not being sent by this airflow sensor so that's what we're gonna look for next see if we can find something like that now with our fuel trim so high it's probably gonna be a pretty big leak if it was a vacuum leak and so we definitely want to look at this tube right here look on the bottom make sure we don't have any cracks or leaks or anything like that make sure everything's sealed up now this looks good and then we'll just continue on looking now here's an intake tube just for example it's not off this truck but as you can see you know this would sit on the vehicle just like this you look at it everything looks fine right we'll look at that that would definitely cause a huge air leak and it would be after your mass airflow sensor if this was a mass airflow sensor vehicle and so you definitely want to look for something like that and so this is your PCB back here right here you want to look at that hose we want to look at these vacuum hoses coming off the intake manifold and you can see they go to some valves over here we want to check all these this pipe right here there's a can you see it there's another tube right here so these are all things we want to look at and make sure we don't see any holes or any problems and as you can see I pulled this off right here and I don't know if you can tell but those are this is all frayed and messed up but we're not gonna get a huge air leak from that it's probably sealing enough where it's not even leaking yet but eventually that's gonna crack enough where it will so this hose will definitely need to be replaced but that's not our problem and you can take a mirror or run your hand feel along these things you know feel if you can feel anything like right there well we got right here huh that's definitely a problem right there and then this thing looks like it's because I'm stay in there not really so that's probably a contributing factor to why yeah this is sliced open it probably got sliced on this thing because it popped off there so that'll have to be fixed now that will allow some air to get in there that's a decent haul but I don't think it's gonna skew our trims more than 30% so we'll put a piece of duct tape or Gorilla Glue on on that and keep moving this is what I use to fix these little hoses on a temporary basis and you see use some black guerrilla tape all right that's the only discrepancy I could find that cut in this vacuum line right here I did repair it temporarily as you can see but I don't believe that this is our problem I don't think that's big enough to create the fuel trims that we are seeing on there while I'm thinking of it you can see like these vacuum ports right here aren't used but you still got to make sure they're capped off so they're not sucking air in and if you're curious about your vacuum routing there's usually a stick or something I'll show you how the vacuum is routed on the vehicle all right I'm done with the visual inspection now I'm safe I can fire up the vehicle and and in this case because our check engine light came on when the vehicles warm I'm gonna let this thing warm up and then we'll look at some data on the on our little code reader now generally when you see high fuel trims and a check engine light at idle usually means some kind of vacuum leak too much air getting into the system but we want to look at our live data as we warm the vehicle up and we want to try to eliminate that if we have a sensor issue or some kind of other fuel delivery issue and so one of the key players is our you can see it our engine coolant temperature sensor you can see we're registering 62 degrees right now and it's about 70 degrees in the shop right now so that's not definitely not out of the ordinary that's that's just fine we can also look at our intake air temperature sensor to which you can see is right down there at 78 so as long as they're fairly close and the vehicles been off for a while then we can be fairly confident that they're both they're both probably working but that engine coolant temperature sensor is a big player in how much fuel the engine is gonna put in there especially when it's cold so basically as the engine warms up keep an eye on that and just make sure it rises and and looks normal one of the first date appears we want to look for which it did almost immediately we want to see our fuel system go from open-loop or o L to seal or closed-loop and that means we're using the oxygen sensors to determine how much fuel and you can see our engine coolant temperatures rising up I think this thing is working just fine and if our freeze frame data would have showed that this came or the check engine light came on when the engine was cold I'd be trying to find a problem before warmed up and if you're curious what vehicle it is what engine it's a 2.4 liter as you can see and it's a two hour ZF email but the things I show you on here pretty much be applied and again all right as you can see we're warmed up we're idling it's idling it feels a bit rough you can see our short-term is maxed out at 19.5% and if I scroll down and our long-term is thirty nine point eight I believe that's the maximum for this vehicle I believe through the combination of the two it won't go any higher all right real quick I'll show you this oxygen sensor this bank 1 sensor 1 it's actually an air fuel ratio sensor that's why we're seeing 3.2 3.3 and basically 3.3 is a perfect 14 point 7 to 1 fuel ratio or stoichiometric and so you can see it's bouncing around right at 3.3 so right now this vehicle is running at a fourteen point seven to one ratio so it's running good it's it's where it's supposed to be but it's having to add a bunch of fuel to get to this point so let's look at the fuel trims at at elevated idle or off idle so there's our short term fuel trim at idle and so what we want to see does it get better or worse or stay the same when we raise it to like 2,000 rpms or something like that and usually if you raise it up and it gets better it's a vacuum leak if you raise it up and it gets worse or stays the same then we either could still have a fuel delivery issue or we have a mass airflow problem so we'll just raise it up [Music] and you can see those fuel trims get considerably better I think we're sure looks like we're dealing with a an air leak somewhere we got a vacuum leak somewhere and go back down to haidle we'll see if it corrects back to 19 you can see its immediately going back to 19 yep so the fuel trims get better with with higher rpms and that usually means it's a vacuum leak because the higher the throttle plate is open the less vacuum inside the system so it's not pulling the pirate air from someplace else and here's our long term fuel trim now this is a learn number over time so when we raise it up if it immediately starts going down that means that it's learned that you know at higher rpms it doesn't need to add as much fuel so let's see if that also confirms our suspicions [Music] yeah you can see that the fuel trims drop so it's definitely learned over the long term that it can drop the fuel trim I think that confirms we're starting to confirm our suspicions that we have a vacuum leak somewhere one that we couldn't see visually all right now we still want to confirm whether we have a fuel delivery issue which I don't think we do but we want to confirm it we can look at our air fuel ratio sensor and at three point three that's pretty much stoichiometric like we talked about before now if it goes under three point three then it's rich if it goes over three point three then it's lean and so we want to we'll hit the throttle and try to make it go down under three point three and that'll show that we have a rich condition and it'll pretty much show that we won't we don't have a fuel delivery problem [Music] and you can see right there we definitely went rich and now we went lean a little bit as it's trying to catch up with the Idol now it's back to stoichiometric now also when we do a snap throttle we should see it go up to like 4.6 or at least over 4 and that what that's doing is a fuel cut and that'll confirm that our oxygen sensor is actually working or in this case air fuel ratio sensor so those are all normal results so let's let's verify it yeah you see I went up to 4.7 4.8 that's the fuel cut it's cutting off the fuel as a you know as part of the strategy when you when it decelerating and so basically we just confirmed that I don't believe we have a filled delivery issue I don't believe we have an air fuel ratio sensor issue it looks like we have a vacuum leak somewhere all right and while I'm here one more important data pit that I like to look at it is the grim per second on the mass airflow when it's warmed up at idle and you can see we're at 1.8 and it's a little low I'd like to see that number a little bit higher in the two to three range but so we'll have to keep that in the back of our mind but right now I'm not too concerned with it but we'll just have to remember that all right let's talk about the long term and short term fuel trims if you don't know what that means well we'll talk about it and in this case we had a four-hour short term a plus 19.5 I think that's what the number was not it was close same thing with the long term it was a plus 39.8 what you do is you add those two numbers together and that's your total fuel trim that's what this is called a fuel trim we're at 59.3% and so basically the computer has a bunch of inputs like the mass airflow sensor and the engine coolant temperature sensor all these inputs are sent in to the engine computer or powertrain computer whatever you want to call it and it has a baseline this is how much this is zero is our baseline and this is how much fuel we should be injecting into this engine based on all the inputs coming in and then once it's doing that the air/fuel ratio sensor or the oxygen sensor depending on what you have in the vehicle in this case this vehicle has an air fuel ratio sensor it's sending an input into the computer that's telling it whether there's too much fuel or not enough and so based on this input right here we're either having to add fuel which would mean positive fuel trend numbers so as the numbers go up like we had on our truck that would be the computer adding fuel and if we saw negative field trip numbers then that would be the computer having to take fuel away from its baseline based on all the inputs so that's in a nutshell of what field trim should be now on a properly operating vehicle you should be able to add the long term and the short term together and you should get plus or minus 10% when you add them together that's a good operating vehicle and we don't need to make any Corrections and it won't set a check engine light in the case of this Toyota anything above 30% short-term and long-term adding them together is going to set a check engine light or anything below minus 35 it's gonna gonna store or set a check engine light and that's of course when you you have to add the short term in the long term together to get those numbers so we have a lot of leeway much greater than the plus or minus 10% that most you know most places will teach you so we do have some leeway but as you can see at 59.3% that's gonna set a check engine light no matter what okay real quick what's the difference between short term and long term why doesn't the computer just have one fuel trim right well basically in order to make the engine run better we want to be able to make quick fast corrections and that's what the short term is there for its job is to make corrections in almost in real time back and forth positive and negative really fast but small corrections to keep it at the proper air fuel ratio the job of the long term is to make this a zero so when when at one point this 39 percent right here was up here on this short term and so what happened get out of here fly you're gonna die fly so what happens is this 39 oh I'm gonna get him I'm gonna get that fly this 39 percent is right here and so after a while when this 39 percent sits on the short-term for a long time then the long term grabs that number and puts it down here so that this can go back to zero and start making real fast short-term Corrections so this long term is learned from this short term over time and so the job of this one is to make this short term as zero so it can make fast Corrections so when this is up at nineteen percent it's it's much harder for it to make Corrections it wants to be at zero so you can just go plus or minus really fast and so I believe this 39 percent is maxed out on this vehicle it won't and it varies from vehicle to vehicle but I believe that's a maximum as a as a safety precaution so we're not just dumping too much fuel into the engine that's the maximum a long term will do and I believe this 19.5% is the maximum combined of what it will do that's why we wouldn't see it go any higher no matter what and so right there is our absolute maximum we can't go any higher and so that's why this number is not zero and this isn't fifty nine point three because the computer has to max it out at some point so real quick those are your long term and long term and short term fuel trims so that you have a better up understanding so now we can go back and look at the vehicle and at least you'll know what I'm talking about now we already did a visual inspection and couldn't find any problems or at least anything then create a huge vacuum leak we fix that little guy right but that wasn't the problem and as you see I got a water bottle here it's the best way to find a vacuum leak in money in many cases not every case but in a lot of cases you can use flammable materials too but you take a chance on catching the vehicle your house on fire so I can and so we'll just spray around all the vacuum hoses and everything and see if we can't find a leak no I'll just spray and see if we can't hear stuff getting sucked in stuff that we couldn't see enough on our inspection and if I suspected a leak between the intake manifold and the engine then I would definitely spray there too but usually those show up when the engine is cold and then as the engine warms up those two pieces of metal expand and seal off any problems so usually to find an intake problem where it's the gasket you got to do it when the engine is just starting to warm up or on a cold engine will spray it anyway just to see if we hear anything getting sucked in but at this point I don't all right sprayed water I don't hear anything getting sucked in no change in the engine RPMs or anything like that so I don't think we have an exponent weak here so now what happens if your evap system you know like your purge they don't call it a purge but it fits basically the first line what if that's stuck open and it's just sucking fumes from the charcoal canister you would think it would drive it rich and it will just for a second briefly but when it sucks all the fumes out of that charcoal canister then it's just going to continue sucking if it's stuck open and it's just going to be sucking air and that air is not going to have any fumes to burn so it's going to create a lean condition so this line right here let's just disconnect it right here I'll put a vacuum gauge on it so we can make sure we have proper deep problem vacuum well we'll look at our fuel trims and see if anything changes and that'll eliminate all this other piping as you can see from our diagram it comes in here goes through this valve goes back to the canister from the canister it comes up to this valve and from this valve that goes over the engine that's why we're just gonna disconnect it from this valve where it goes right to the engine will eliminate all the rest of this crap all right I'm just gonna take this vacuum and pressure gauge this one's from OTC I have it some adapters on here so I can adapt to that hose right there we'll just make sure we have proper vacuum which is anywhere from you know 16 17 up to 21 or 22 right in that range with the vacuum on most vehicles when its operating properly and then we'll check our fuel trims afterwards to see if there's any change but then we'll have sealed the system from there off oh she didn't like that all right as you can see where it's sitting at about what 18 18 and a half so it looks like our vacuum is pretty perfect not nothing wrong there now let's go look at our fuel trim to see if we made a correction as you can see if you didn't if you're not following what I'm doing I just have this sealed off with the vacuum gauge so now everything we're checking everything after this point to make sure there's no leak and obviously we're checking this too because if there was a leak we'd probably see a little bit lower vacuum but you don't I think getting back in with that was right here is not fixed with this gorilla face all right and looking at our right as you can see our short term fuel trim has not changed still sitting at the bottom there 19.5% and to make sure our long term hasn't changed be nice if we could see both of these on the same screen it's still at 39.8 so we'll leave it here for another minute or two to make sure it doesn't take a second to correct but at this point does not look like we found our problem all right I left it there for a minute fuel trims have not changed so this is not our issue I'll go ahead and put this back all right the other big main line coming into our intake would be this hose right here going to our brake booster so I'm gonna disconnect it right there we'll do the same test now that hose is fatter so this one's probably not going to work to put a little bit fatter adapter on that then we'll check oh she didn't like that either dan let's look into our vacuum is slightly better closer to nineteen but almost exactly the same so our vacuum looks good from this point also now let's go check our fuel trim see if we have any correction all right now look at our short term fuel trim drop down to almost negative five and there's a negative five we dropped twenty five look at that twenty six points just like that I think we have a problem with our brake booster and as you can see our long term is still at thirty nine point eight percent but that's because it's a learned value so if we let this engine run with with the vacuum leak fixed eventually that's gonna start to go lower too and correct itself but it would take a while and probably we'd have to drive it a little bit and you can see just sitting here a long terms already starting to correct and you can see our air/fuel ratio is just a little bit under three point three and so it's definitely running slightly rich it's gonna take a little while for this engine computer to figure out what's going on and make the corrections alright now I broke out the big auto tell just so we could look at everything on the same screen we can't do all this stuff on the other one also but you can still see even with this fix we're at thirty three percent and one so we're still at about almost thirty five percent actually just about thirty five percent positive fuel trim so we still have an issue and if you remember our mass airflow was at about 1.7 1.8 a little while ago and now we're at 2.2 and just a before I've turned the camera on it was at about two point eight I think we might still have an issue with the mass airflow not reporting exactly and these things it's very critical this mass airflow sensor if it doesn't report exactly it's just off by a little bit it'll throw the engine computer off so see if we can't do a few more checks on this mass airflow sensor now I'd like to see this mass airflow a little bit higher seems like it's slightly low from my area and these are learned numbers you need to learn it I mean two to three is a good range but I would like to see that closer to three here at idle where I live I suspect it was a little bit lower before we fixed that few huge vacuum leak and that was it was skewing the numbers just sucking so much air from the brake booster who was throwing that number down a little bit so I wasn't as concerned but I would like to see it up just a little bit higher now let's bring it up this up to about 2500 rpms and see not only what our fuel trims do see if they stay the same get worse or get better and let's see what this grams per second is in my area I want to see closer to nine to ten right in that range on the mass airflow so let's bring it up to twenty-five hundred [Music] you can see our fuel trims are almost the same not a huge difference they're still pretty bad and they're g/s just like that idle it's a little bit low I don't like that I think we have a problem with our mass airflow underreporting just a little bit and that's enough to throw these lumbers off [Music] and you can see our numbers are pretty close to the same at idle now I already cleared the codes and then ran it again when I plug the autel in so let's see what what spending because the check engine light isn't on but I could see that we had a fault so let's look at it real quick and you can see we still have a p0 171 even though we've fixed a huge problem and dropped it down like 25 points we still are over 30 which is gonna set that check engine light on this vehicle so and this is a to trip code so that's why it's pending we would have to turn turn the vehicle off turn it on a second time and get those trims up those fuel trims to high above 30 and then this would set a permanent code that's why it's still pending all right we're gonna check the signal on our mass airflow real quick and what we're gonna check is this e to G and the VG that's our signal wire the VG is our signal E to G is going to be our signal ground so from the mass airflow pins 4 & 5 we're looking for the black with white and the gray wire pins 4 and 5 will back probe those two and look at our signals alright as you can see I have pins 4 & 5 back probe right there on the mass airflow sensor and I have it hooked up to the Vantage ultra I could use my little AES way view scope tube but we need some kind of scope to see the signals because they're too fast for a for a DV om and so right now with the key on but the engine off we're at 0.32 volts and so we'll fire it up and we'll do a snap throttle test and we'll check out the pattern see what it looks like alright now we're just gonna do a couple snap throttles and see what it looks like alright here's our signal from the from that snap throttle test and as you can see here's our initial rush of air going in then it drops just a hair then it goes back up to our peak and then comes back down so that's a normal-looking signal I don't like this hash in here but but that's a normal-looking signal as far as the pattern and also we only hit a maximum of three point five one was like three point three and one was three point five I'd like to see that just a little bit higher closer to four if we could so I definitely suspect that there's an issue with this mass airflow sensor just underreporting slightly which is enough to throw our fuel trims off and like I said I could have easily used this AES wave you scoped to cope the signals but I wanted to use this because it's a little bit easier to see on video alright got a brand new mass airflow sensor from Toyota installed and you can already see that the voltage is a little bit higher just sitting here with the engine off let's go look at the data alright as you can see with the engine off our mass airflow sensor is 0.57 just like the old one was so let's fire up this vehicle see what the fuel trims in this comm g/s look like with it on now our engines not quite warmed up so our engine speeds a little bit higher but look at that look at our short trim short term fuel trim it's already dropping like a rock in our long-term look it's already dropped to 5% and a -3 this thing has already fixed itself hasn't even gotten warmed up yet all right now we're over at an idol we can see that our grams per second on the mass airflow is right around three just a hair under three or just a hair over there right about three that's definitely a little bit better and then look at our fuel trims short-term is at 1.5 long terms at 0.74 that's definitely a fixed that's well within our plus or minus 10% as our general rule of thumb and it's well under the 30% that'll set the check engine light on this vehicle so there you go that's a confirmed fix this thing needed a new brake booster and a mass airflow sensor and as I raise the title up you can see our short our short term has having to correct for the long term see the long term at 28% in our short term is minus 20 because this long term is a learn number and it takes a while to get it to go down actually this one's correcting pretty fast but yeah you can see how fast that's correcting and while we're here let's look let's get our engine speed up to 2,500 and look at our grams per second on the mass airflow [Music] [Music] there you can see we're right about 2500 and we're 9.5 definitely definitely looks much better than before that mass airflow is just underreporting by a little bit which is enough to throw this vehicle off [Music] and you see when we go back down to idle fuel trims almost perfectly zero and it's going to fluctuate a little bit you can see we're very close to zero this is this vehicles fixed alright now we'll do a couple more snap throttle then we'll see how the signal looks this time [Music] and look at that one although there was some hash in there look what we maxed out at we maxed out at four this one's looking good all right so here's here's what the new mass airflow sensor you can see we still they have the same initial rush of air and it drops down and we do have a little bit of hash just like the old one but here's where it really shines we get this nice secondary rush of air and we're up to four volts and then it drops back down nice and clean that is definitely a much better looking waveform and that's a confirmed fix alright with the new mass airflow but with the old brake booster back connected but still look at our fuel trims now all right you can see where our numbers are at long-term is at plus fifteen short-term is at plus three so you can see we're almost eighteen nineteen percent and you can see our mass airflow grams per second or just a hair lower than they were before probably because of this big vacuum leak that we've created it's throwing off the airflow just a little bit so you always got to keep that in mind that a huge vacuum leak might throw your mass airflow sensor off just a little bit in an idle all right let's raise the RPMs and see what our fuel trims do if they get better that would confirm a vacuum leak which we already know we have one [Music] and you can see our fuel trims got considerably better 7 + -2 -3 yeah you can see we definitely have a huge vacuum leak out of that brake booster all right now let's keep an eye on our short term fuel trim we're almost at 20% but on our short term let's see what happens when we step on the brakes create an even bigger vacuum leak all right foots on the brake you can see our short-term just went up to 20% so we created an even bigger vacuum leak so that definitely confirms our suspicions that we have a bad brake booster I just let off of it and you can see it goes back down and stabilizes so this vehicle also needs a brake booster so as a quick recap air comes in you know and is used by the engine and the amount of air that goes in is measured by this mass airflow sensor and told to the computer and so in our case it was falsely reporting it was under reporting by a little bit which was causing our fuel trims to go up so the computer was having to add fuel and we had another problem with the brake booster where that the internals failed on it and it was sucking air into the engine so this air that was coming from here was unmetered by the mass airflow so that was even compounding the problem so we had a mass airflow that wasn't reporting properly and we had additional huge air leak going into the engine and so that was causing massive amounts of air into the engine more than the fuel that was going in there and so computer was having to compensate so you always have to remember just because you find one problem there might be another one all right now I need to get a new brake booster and get it put on there and as always the video helped you liked it make sure to give it a thumbs up thanks for watching [Music]

Channel: Big Dog50001 Automotive

Views: 1,133,132

Rating: 4.8056474 out of 5

Keywords: how to fix P0171, toyota P0171 diagnosis, toyota system too lean, P0171 system too lean repair, how to diagnos P0171, toyota check engine light, CEL P0171, big dog 50001, big dog50001, DIY repair P0171, mass air flow problem, vacuum leak, brake booster air leak, poor idle P0171, mass airflow sensor, brake booster bad, vacuum leak causes p0171, bad MAF sensor causes p0171, DTC p0171, P0174, scan tool, p0171 p0174, diy auto repair, check engine light, code p0171

Id: SugtR4KMIDU

Length: 46min 18sec (2778 seconds)

Published: Wed Jan 09 2019