P0171 Trouble Code: System Too Lean Bank 1 Diagnosis and Repair!

hello viewers welcome to k diagnostics duo here today we have a 2007 toyota corolla with a 1.8 liter the customer complaint on this vehicle is the check engine light remains on while the engine is running so the first thing we're going to do is we're going to confirm the customer's complaint after confirming the customer's complaint we're going to connect the scan tool to the vehicle to see what kind of trouble codes we have in the indian computer so now let's go inside the vehicle and confirm the customer's complaint all right so i'm gonna start the engine so that we can confirm the customer's complaint so let's start the engine and see if the check engine light will remain on so right there as you can see the engine is running and the check engine light remained on so customer's complaint confirmed [Music] so right there the check engine light remained on so now i'm gonna turn off the engine i'm gonna turn the key to the on position i'm gonna get the scan tool connected and then i'll bring you guys back up all right so i got the scan tool connected so now let's scan this vehicle so this is a toyota all right guys so right here we have five trouble codes in the engine computer but as i'm going through these trouble codes here it looks like we only have two trouble codes the first trouble code is p0171 so it's a current code and it says system two lien bank one and then the second trouble code is p0420 it's a pending code so this is about a cuddly converter and it says catalyst system efficiency below threshold so this code over here is a pending code it's also a current code and this p0171 trouble code it's the same code up here but here it's a current code and over here it's a history code so it means this trouble code was here in the past and it's also present as we speak and same thing with this second trouble code over here so basically we just have two trouble codes okay now i'm gonna focus on this p0171 trouble code first because this trouble code being there the problem that's causing this trouble code to be set will damage totally converter okay because if we have an engine that's running lean if we have excess air that's not being mirrored by the mass airflow sensor getting inside the intake the computer is not going to see that air okay it's just going to see a lot of it through the oxygen sensor and when the computer sees a lot of oxygen in the exhaust stream it's going to adjust that so it's going to adjust the pulse width so meaning it's going to add more fuel inside the cylinders okay and more fuel it means the engine is going to run slightly richer because the computer will try to compensate for that excess air which can eventually damage the catalytic converter okay because if we pump too much fuel in the cylinders all that fuel it's not going to get burnt you will still have a little bit of fuel that's going to get pushed into the exhaust stream and if you have fuel that's being pushed into the exhaust stream it will eventually get to the catalytic converter and then burn it okay so this trouble code this p0171 trouble code caused this catalytic converter to go bad okay now this p0171 code can be caused by a couple of things okay this can be caused by a vacuum leak if we have unmetered air that entering the engine between after the mass airflow sensor and the intake that can cause this trouble code to be set if we have a dirty mass airflow sensor a dirty mass airflow sensor can also cause this trouble code to be set uh low fuel pressure problems can also cause this cause to be set even a skewed o2 sensor can cause this trouble code to be set so there are a couple possibilities that can cause this p0171 trouble code to be set so now what we're gonna do is i mean we could have also seen uh clogged injectors cause this trouble code to be set so now what we're going to do is we're going to focus on this trouble code like i said we have to find out what's causing this trouble code and once we figure out what's causing this trouble code then we will worry about this p0420 okay so about the p0420 we're gonna check the o2 sensors the one before the catalytic converter and the one after the catalytic converter if both sensors check out okay then we will replace the catalytic converter but we have to make sure we fix this p0171 trouble code first okay so uh right now the next step will be looking at live data but before i do that i want to look at my freeze frame data first let's look at the freeze frame data because i want to know what the computer was looking at when these trouble codes set i want to look at the engine speed i want to pay attention to the engine speed to know when this trouble code set as you can see the engine speed was 700 rpms so this set at idle so when this trouble code set the engine speed was 700 rpms and i'm pretty sure the vehicle was stationary so our short term was 5.43 and then our long term right here our long term was 31.98 okay and this was at idle so as you can see vehicle speed was zero so this was stationary so i have 31 percent on the long term that lean code will be set because the normal range on an engine that's working well the fuel trim is plus or minus 10 so once you start to go past that i mean that's kind of the rule of thumb but once you start to go past that a trouble code will be set so let's go to live data now what i want to do is i'm going to select a couple data that i want to look at so right over here we're gonna focus on the fuel trim numbers so short term and long term and also the engine speed and the mass air flow sensor reading and the o2 sensor readings okay so now i'm going to start the engine right now what i'm looking at is i don't want these numbers being too high if you see high positive numbers you see this number over here on the long term we have 19.49 percent and on the short term we have minus 0.04 so on the long term we have positive numbers if you don't see a sign here it means that's a positive number and on the short term we have negative numbers now nineteen percent is high like i said the rule of thumb is plus or minus ten so when you see a high number over here on the long term or the short term that means the computer is adding more fuel to compensate for the excess air okay now what we need to figure out is the excess air where is that coming from do we actually have a leak or do we have a sensor that's under reporting okay we can have a dirty mass airflow sensor that can cause these numbers to be high we can have a fuel delivery problem we could also have an oxygen sensor problem so the list can go on and on and on so now i'm going to start the engine we're going to watch these numbers and see we need these numbers short term plus long term we want these two numbers together if we add them together to be at plus or minus 10 percent okay so now i'm gonna start the engine so the engine is running we're still in open loop so let's let it idle a little bit until we go into closed loop so right there we are in closed loop so our short term is starting to correct so if we add these two together so we have 3.09 and 19.49 so if we add these two we have about 22 okay total trim which is a lot now let's look at the mass airflow sensor our mass airflow sensor is reporting 2.1 it's going between 2.48 and 2.5 grams per second i mean this is a 1.8 liter so this number should have been slightly lower than this let's look at our o2 sensors so i'm going to graph these o2 sensors so over here on the second o2 sensor the one after the catalytic converter we have a straight line which is pretty good because we don't want to see a lot of activity on the second o2 sensor but the first one i don't like how we have a flat line here on the first one i mean this could be because these sensors are not hot yet because sometimes these sensors have to get really hot before they start to work so we're kind of gonna ignore these for now we'll check this later so let's focus on these fuel trim numbers short term and long term now here's what i'm going to do uh as you can see our engine speed is 748 rpms and on the short term we have uh the short term we have 3.09 percent and the long term is 21 yeah so this is too high our numbers are definitely out of whack so what i'm gonna do now is i'm going to increase the engine rpms and as i increase the engine rpms we're gonna watch these numbers to see if these numbers will get better if i increase my engine speed up to 3000 rpms and these two numbers come down if we have plus or minus 10 percent on total fuel trim so short term plus long term if we have 10 percent here that will tell me that our problem is most likely a vacuum leak because if we have a vacuum leak a vacuum leak would impact an engine at idle not at high rpms because when you increase the engine rpm the throttle opens so you don't have vacuum inside the intake manifold so a vacuum leak would not cause these numbers to be high at high rpms okay what would cause these numbers to be high at high rpms is low fuel pressure a bad o2 sensor or a clogged injector and and the list can go on and on and on so um now i'm going to increase the engine rpms and let's watch so watch our engine speed here so we're gonna go up to three grand so right there three grand so my short term number is going down so look at my uh i mean my long term number i'm sorry my long term number is going down and so is my short term number so let's hold it there so i'm gonna let off so once i let off we come down to idle our long term goes high okay we have high numbers on the long term so now let's check these o2 sensors so it looks like our o2 sensors are switching so now what i'm gonna do is i'm gonna i'm gonna try to drive these o2 sensors lean so i'm gonna do that by pumping on the brake pedal to drive this engine leaner to see how quickly these o2 sensors will react so i'm gonna do that as you can see right there we just dropped here so this one went up okay so on the o2 sensor the the air fuel ratio one the one before the catalytic converter a high voltage so about four volts is a lean reading and then the one after the catalytic converter a low voltage so we have 0.015 volts okay so we're driving these o2 sensors lean so they can definitely respond to the oxygen content in the exhaust stream so i'm going to let off and you will see this one will go up and this one will go down so right there you saw that so i just let off so our o2 sensors are most likely working okay you saw as that one went up and that one uh went down so that's good okay these o2 sensors are good so once we fix whatever that's causing this lean trouble code to be set we can just go ahead and replace the catalytic converter this vehicle will be fixed okay wow check this out we have thirty four point 33 on the long term this is crazy so let's increase the engine rpms again so right there so when we increase our engine rpms [Music] our long term goes down so that's good and once we come back to idle our long-term numbers go high so let's go under the hood test this for a vacuum leak and if we don't have any vacuum leaks we're going to look at the mass airflow sensor we're gonna inspect it if it's dirty we're gonna clean it and this problem will be fixed so let's go under the hood and check for a vacuum leak first so i'm gonna turn off the engine so let's get this out of here let's go under the hood and check for a vacuum leak all right guys so we are here under the hood we're gonna check for vacuum leaks but before we check for any vacuum leaks i want to look at this mass air flow sensor first since we have high long term numbers we have high positive numbers on the long term i want to remove this mass airflow sensor and inspect it because if we have a dirty mass airflow sensor our fuel trim numbers won't be good okay i know a dirty mass airflow sensor tends to cause high positive numbers at high rpms i don't know if you can see in there but those resistors look not too bad i don't know if you'll be able to see those resistors in there are not really dirty i'm going to clean them but i still believe we have a vacuum leak okay so i'm going to remove this cover i'm gonna remove this cover and then we're gonna get a uh we're gonna get a vacuum machine and we're gonna smoke this intake to see if we have a vacuum leak somewhere already so it looks like these ignition coils been replaced pretty recently because they look new all right so i'm gonna clean up the mast airflow sensor i mean the resistors on the mast airflow sensor don't look really dirty i'm gonna clean them up and then i'll bring up our vacuum machine here i mean our smoke machine so that we can smoke this intake so i will get the smoke machine set up and then i'll bring you guys back up all right guys so i got my smoke machine out and ready to go i'm sorry i have a a little air leak back there so that's gonna be a little noisy so we're gonna connect our smoke machine to the battery now i disconnected the hose that goes to the brake booster so this is where we're gonna send our smoke okay so it's gonna go through this hose and into the intake so i didn't want to attach anything here the only thing i removed was the mass airflow sensor that we looked at the mass airflow sensor doesn't look really dirty the resistors on the mass airflow sensor don't look too dirty so i don't think that's what's causing these long-term numbers to be really high so i am going to turn this on so we're gonna send smoke into this hose and then we will observe around the engine to see what smoke is gonna come out of let's give this a couple minutes so as you can see our smoke is starting to come out so that's good we have smoke right there so now we're gonna connect it to this hose okay so we connected it to the hose so now let's watch oh it's coming out of here there's your leak now so we have to find a way to block this i didn't want to remove this but i guess what i'm gonna do let me turn this off first so what i'm gonna do is i'm going to remove this clamp and block this off and then we will turn on our smoke machine again so i will remove this clamp i will disconnect this air tube from the air filter box and then i'll block this off so we can prevent smoke from going to the air filter box so i will do that and then i'll bring you guys back up all right guys so i turned the smoke machine on again so i'm plugging this side of the inlet tube so kind of ignore the smoke coming from this side but i see a leak over here there's a leak on this tube okay this pcv tube over here it looks like someone had fixed this and this is really loose okay and this can cause a vacuum leak because if we follow this tube this tube goes straight to the intake okay ignore the leak around this because this is not really sealing properly but besides the leak over here there is no other leaks around the intake manifold okay so i'm going to turn off my smoke machine and then we're going to fix this leak we're gonna fix it we're gonna start the engine and see if our fuel trim numbers will get better after we fix this so i'm gonna turn off my smoke machine so i'm gonna remove this and then i'll bring you guys back up all right so smoke machine is turned off let's remove this cap okay i doubt if this is the only leak but let's address that first so someone had put this piece over this and if you look at this tube this tube over here has a pretty big crack okay so this can cause a vacuum leak i'm going to cut this off i'm going to try to fix it i'm going to try to fix it and then uh i'm going to cut this off and i'm going to push this in to see if it's going to fit and then we will start the engine to see if our fuel trim numbers will get better so i will do that and then i'll bring you guys back up you see this crack over here yeah this thing is pretty cracked all right so i will fix that and then i'll bring you guys back up all right guys so i fixed this pcv tube so right over here i put a hose there and a little fitting so this is good it's not gonna leak anymore i also cleaned the mass airflow sensor i put it back on everything is back together i'm just gonna have to tighten this clamp this tube over here was cracked someone had put this there so i had to cut it off so i did cut this off okay so this crack over here was letting excess air to go through this tube and into the intake manifold so i cut that off i put a brass sleeve between this tube and this hose i put over here so this is tight it's not going to leak anymore and then we're going to go inside the vehicle and start the engine we're going to look at a few trim numbers to see if our fuel trim numbers will get better i don't know if it was as simple as this but let's start the engine and see what happens because that crack on the tube could have caused a pretty big vacuum leak also so i'm going to tighten this clamp and then we're going to go inside the vehicle we're going to start the engine and we will watch our fuel trim numbers so i will do that and then i will bring you guys back up all right so we're back in the vehicle i'm going to start the engine so the engine is running i'm gonna bring up our scan tool so we are in closed loop but we still have high numbers on the long term i mean hold on let's see let's watch it a little bit let's see if these numbers will drop we have minus seven percent on the short term which is good so minus eight so that would take us down to about eight percent total trim i kind of like these numbers i'm seeing here right now let's observe it a little bit longer [Music] so -10 but i don't like how high this number is staying though the long-term percentage okay it's dropping so that's good okay that's good we're dropping so that's good i like these numbers now okay so this is pretty good so right now we have about eight percent total trim i mean short term plus long term we have about eight percent which is good i mean you saw before our numbers were really high so that's really good let's look at our o2 sensors our o2 sensors are switching so look at our long-term and short-term fuel trim numbers so we have about 10 percent so now i'm going to increase the engine rpms and look at our mouth so i'm gonna let off so the mass airflow sensor value is basically the same we had about 2.3 or 2.4 when we first started but i like these numbers guys i like these numbers okay i do like these uh numbers that we have so i guess the problem was that pcv tube the crack on the pcv tube was causing a vacuum lick which caused this p0171 trouble code to be set and as you can see right now um our numbers look better because if we add this with this one we have about roughly 10 percent [Music] so that's good guys um i'm going to leave this right over here we definitely fixed this so the problem was a cracked pcv tube so at this point i can go ahead and replace the catalytic converter because there's also that p0420 trouble code and our o2 sensors are working fine so i can go ahead and replace the the catalytic converter with the numbers i have feel comfortable replacing the catalytic converter i'm okay with these numbers this p0171 trouble code is fixed so the problem was a cracked pcv tube okay i like the numbers we have now we are definitely within a normal range so this is fixed guys our o2 sensors also work fine i'm going to call the customer to ask if he's going to give me the go ahead to also replace the catalytic converter if it gives me the go ahead i'm gonna go ahead and replace the catalytic converter also okay i feel comfortable about these numbers okay so 10 on the long term is good i'm gonna turn off the engine so that's it guys this was a quick and easy one the problem was a vacuum leak caused by a cracked pcv tube so i'm gonna leave this right over here guys i hope you like this video if you do like the video give it a thumbs up if you don't give it a thumb down but if you do you gotta tell me why so we can make better videos in the future if this is your first time here subscribe to the channel ring the bell so you can get notified every time i upload a new video if you have any questions criticism leave them in the comment box thanks for watching guys see you next time

Channel: KIT'S Auto and Truck Repair

Views: 226,340

Keywords: code P0171, how to diagnose a p0171 trouble code, P0171 system too lean diagnosis and repair

Id: WW1hJJI5BJc

Length: 31min 11sec (1871 seconds)

Published: Tue Sep 14 2021