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

so you have a check engine light and you scan it and you find that you have a p0171 or p0174 which is a low fuel trim let's talk about it so here's some quick and easy things you can check that could have caused that problem or can potentially fix it you want to find under the hood where the air box is located your air filter is in here and that's gonna that is where the engine gets the air to breathe you need air and fuel to make the engine run so you need to filter that air so off that air box you're gonna find a snorkel that goes directly into the engine you want to grab that give it a shake see if anything's loose like over here like if this is loose that's not good near the air filter you're going to have something called a mass airflow sensor now that's going to tell the computer how much air is getting into the engine and the computer needs to know so that it can dump more fuel in or less fuel depending on that but if you're getting extra air coming in through here it's not measuring that fuel going in so that's going to give you a code so you could have replaced the air filter or someone could have replaced the air filter for you and just forgot to tighten this up it happens all the time anything loose like that you just tighten it up should be able to clear the code and you'll be on your way so on a different vehicle the air box is right here where the air filter is there's the wires and if you follow the snorkel there's actually a hose that's supposed to be right there if that was left off that's going to cause that code or even if you check and see it's disconnected right there that needs to be hooked up hook that up and clear the code so again this is a different vehicle air box right there nas airflow sensor right there and just check the tubes you know you also want to check any of this rubber there could be a crack in there and that could cause it as well sometimes these have to be replaced but definitely check the hose underneath here you may have to lift an engine cover up take a look just make sure everything's connected all right so now let's get underneath the engine cover if many vehicles have little covers over the engine and all you have to do is lift them up some of them may have a screw in them so you want to look at the hoses that are connected to the intake anything and just make sure nothing's disconnected everything's attached you know if you had some engine work done recently and there's a hose that's not connected now you want to check any ports if any ports seem like they're open make sure that it's not something that's plugged off because that's not going to cause an issue but something like this where it's open should have a hose on it or something or even a plug covering it so if you don't see anything visual what you can do is start the engine up and stay away from any of the moving components and try to listen for a whistle type noise or air rushing and then just try to feel around see if you can plug something off if any of the pitches change if you plug off one of these holes and it changes then that can help you find the leak and also any of these lines if there was a pinhole in the line you may be able to find it that way as well let's take a quick look at the air filter your air box may have clips or screws holding the air box down just take the air filter out take a look at it this one's pretty dirty now that's not going to cause the code but if you had a hole in here where some debris can get past the air filter itself that's important that you change that and while you have the air filter out you can see the mass airflow sensor now i've seen in the past where you'll have a leaf actually get by the air filter and it's in front of the mass airflow sensor and that can cause some issues or any type of debris it could get dirty and that could cause this code so not a very common problem but it could potentially be the mass airflow sensor if it's dirty or sending a bad signal to the vehicle's computer and giving you that faulty code so those are some of the quick and easy simple things you can check out let's get a little more advanced so everything after the mass airflow sensor into the engine block itself has to be sealed and all the hoses connected well you could also have you have your intake plenum right here you actually have gaskets in between the plenum and the heads themselves now those gaskets could leak they could be broken they could be cracked and if those leak you're definitely going to get a low fuel trim code now we have a bunch of videos on how to replace intake gaskets every vehicle is a little bit different you can check those out try to attempt that yourself it's that if that's a little more advanced you can take it to a professional so you may notice the engine runs very rough and there could be a large leak and something like if there's a bad seal on the purge valve or something you can hear that leaking right now just like that but you may notice the engine stumbling running really rough another thing we can do is take some carburetor cleaner or throttle body cleaner and you can take it while the engine is running and you can actually feel the engine running rough and as you spray it all along the areas that you think you might have a leak at the intake you can notice the engine either run smoother or rougher or even have someone watching the gauges and watch the gauges fluctuate as you're spraying and that's a good indication to find where the actual leak is so what we can do is if we take the scan tool or the code reader and we can find select engine speed confirm now while you're monitoring the engine speed if you have the ability to graph the engine speed so and then we're going to take some carburetor cleaner now remember this is flammable you don't want to spray this near the alternator or anything electrical you don't want to spray it near the coils or anything but if you spray it just on the intake gasket itself or where you think you may have a leak like if you sprayed it in that area down there where we have our leak right here as you're monitoring the engine speed so we notice the drop in revolutions per minute the engine speed that's where our leaks going to be the engine's running rough now you may see it actually go the other way you may see the engine speed go up as long as you see a difference that's probably where your leak is everything we've talked about so far has to do with the engine getting air and everything being sealed up in the intake system so everything after the mass air flow sensor has to be sealed up to the engine now there could be two additional problems that could cause this code you could have a fuel injector issue or an o2 sensor issue so your fuel injectors are located right here and they're attached to a fuel rail and there needs to be a certain amount of pressure in this fuel reel so if that pressure is not high enough you're not going to get enough fuel and that's your air fuel mixture is not going to be correct that could cause that code so if there's not enough pressure there or if the fuel injector itself is plugged up it's not letting enough of that fuel get into the engine same deal so the engine's not seeing enough fuel in that situation and it's trying to add more fuel and it's unable to do so that's going to set that code related to the fuel pressure being low you could have a bad fuel pump not putting enough pressure there or even a fuel filter that's partially plugged up not getting enough fuel there or the oxygen sensors now there's four oxygen sensors on this vehicle there's two in the front and there's two that are further down the exhaust the ones in the front are the ones that we're concerned with those are the ones that are going to monitor the engine's fuel air ratio so any unburned fuel or air gets into the exhaust and that o2 sensor will monitor that and send the signal to the computer and make adjustments well if this o2 sensor isn't sending the correct signal to the computer that's going to cause an issue i hope this video helps you out if you enjoyed it please subscribe to our channel make sure you ring the bell turn on all notifications so you don't miss any of our videos you

Channel: 1A Auto: Repair Tips & Secrets Only Mechanics Know

Views: 188,142

Rating: 4.8977408 out of 5

Keywords: check engine code, obd trouble code, diagnostic trouble code, p0171, p0174, system too lean, bank 1, bank 2, how to, diy, car repair, 1a auto, do it yourself, intake leak, vacuum leak, bad fuel injector, bad 02 sensor, bad o2 sensor, bad oxygen sensor, running lean, rough running engine, lean air fuel mixture

Id: tPZb1uWu9oo

Length: 9min 14sec (554 seconds)

Published: Thu May 28 2020