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Check Engine Light? System Too Lean - Code P0171 or P0174 on Your Car or Truck - YouTube
Channel: 1A Auto: Repair Tips & Secrets Only Mechanics Know
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so you have a check engine light and you
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scan it and you find that you have a
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p0171 or p0174
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which is a low fuel trim let's talk
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about it
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so here's some quick and easy things you
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can check that could have caused that
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problem or can potentially fix it
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you want to find under the hood where
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the air box is located
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your air filter is in here and that's
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gonna
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that is where the engine gets the air to
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breathe you need air and fuel
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to make the engine run so you need to
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filter that air
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so off that air box you're gonna find a
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snorkel that goes directly
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into the engine you want to grab that
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give it a shake see if anything's loose
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like over here like if this is loose
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that's not good
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near the air filter you're going to have
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something called a mass airflow sensor
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now that's going to tell the computer
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how much air
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is getting into the engine and the
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computer needs to know
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so that it can dump more fuel in or less
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fuel
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depending on that but if you're getting
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extra air coming in
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through here it's not measuring that
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fuel going in
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so that's going to give you a code so
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you could have replaced the air filter
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or someone could have replaced the air
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filter for you and just forgot to
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tighten this
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up it happens all the time anything
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loose like that you just tighten it up
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should be able to clear the code and
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you'll be on your way so on a different
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vehicle
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the air box is right here where the air
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filter is there's the wires
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and if you follow the snorkel there's
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actually a hose that's supposed to be
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right there
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if that was left off that's going to
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cause that code or even
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if you check and see it's disconnected
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right there that needs to be hooked up
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hook that up and clear the code so again
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this is a different vehicle
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air box right there nas airflow
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sensor right there and just check the
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tubes you know you also want to check
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any of this rubber there could be a
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crack in there
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and that could cause it as well
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sometimes these have to be replaced
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but definitely check the hose underneath
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here
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you may have to lift an engine cover up
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take a look just make sure everything's
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connected
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all right so now let's get underneath
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the engine cover if
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many vehicles have little covers over
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the engine
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and all you have to do is lift them up
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some of them may have a screw in them
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so you want to look at the hoses that
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are connected to the
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intake anything and just make sure
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nothing's disconnected
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everything's attached you know if you
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had some engine work done
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recently and there's a hose that's not
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connected
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now you want to check any ports if any
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ports seem like they're open
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make sure that it's not something that's
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plugged off because
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that's not going to cause an issue but
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something like this where
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it's open should have a hose on it or
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something or even a plug covering it
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so if you don't see anything visual what
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you can do is start the engine up
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and stay away from any of the moving
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components and try to listen for a
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whistle type noise or
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air rushing and then just try to feel
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around
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see if you can plug something off if any
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of the pitches
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change if you plug off one of these
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holes
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and it changes then that can help you
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find the leak
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and also any of these lines if there was
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a pinhole in the line
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you may be able to find it that way as
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well let's take a quick look at the air
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filter
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your air box may have clips or screws
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holding
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the air box down just take the air
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filter out
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take a look at it this one's pretty
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dirty now that's not going to cause the
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code
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but if you had a hole in here where some
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debris can get
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past the air filter itself that's
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important that you change that
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and while you have the air filter out
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you can see the mass airflow sensor
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now i've seen in the past where you'll
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have a leaf actually get by the air
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filter
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and it's in front of the mass airflow
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sensor and that can cause some issues
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or any type of debris it could get dirty
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and that could cause this code
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so not a very common problem but it
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could potentially be the mass
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airflow sensor if it's dirty or sending
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a bad signal to the vehicle's computer
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and giving you that faulty code so those
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are some of the quick and easy simple
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things you can check out let's get a
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little more advanced
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so everything after the mass airflow
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sensor
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into the engine block itself has to be
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sealed and all the hoses
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connected well you could also have you
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have your intake plenum right here
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you actually have gaskets in between the
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plenum and the heads themselves
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now those gaskets could leak they could
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be broken they could be cracked
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and if those leak you're definitely
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going to get a
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low fuel trim code now we have a bunch
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of videos on how to replace intake
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gaskets every vehicle is a little bit
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different you can check those out
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try to attempt that yourself it's that
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if that's a little more advanced you can
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take it to a professional
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so you may notice the engine runs very
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rough and there
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could be a large leak and something like
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if there's a
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bad seal on the purge valve or something
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you can hear that leaking right now
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just like that but you may notice the
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engine stumbling
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running really rough another thing we
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can do is take some carburetor cleaner
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or throttle body cleaner and you can
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take it while the engine is running
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and you can actually feel the engine
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running rough and
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as you spray it all along the areas that
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you think you might have a leak
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at the intake you can notice the engine
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either run smoother or
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rougher or even have someone watching
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the gauges
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and watch the gauges fluctuate as you're
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spraying and that's a good indication to
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find where the actual leak is
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so what we can do is if we take the scan
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tool
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or the code reader and we can find
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select engine speed confirm
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now while you're monitoring the engine
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speed
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if you have the ability to graph the
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engine speed
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so and then we're going to take some
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carburetor cleaner now remember this is
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flammable you don't want to spray this
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near the alternator or anything
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electrical you don't want to spray it
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near the coils or anything
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but if you spray it just on the intake
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gasket itself or where you think you may
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have a leak
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like if you sprayed it in that area down
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there
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where we have our leak right here as
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you're monitoring the
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engine speed
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so we notice the drop in revolutions per
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minute
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the engine speed that's where our leaks
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going to be
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the engine's running rough
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now you may see it actually go the other
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way you may see the engine speed go up
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as long as you see a difference that's
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probably where your leak is
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everything we've talked about so far has
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to do with the engine getting
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air and everything being sealed up in
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the intake system so
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everything after the mass air flow
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sensor has to be sealed
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up to the engine now there could be two
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additional
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problems that could cause this code you
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could have a fuel injector
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issue or an o2 sensor issue so your fuel
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injectors are
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located right here and they're attached
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to a fuel rail
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and there needs to be a certain amount
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of pressure in this fuel reel
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so if that pressure is not high enough
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you're not going to get enough fuel
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and that's your air fuel mixture is not
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going to be correct
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that could cause that code so if there's
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not enough pressure there
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or if the fuel injector itself
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is plugged up it's not letting enough of
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that fuel get
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into the engine same deal so the
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engine's not seeing enough fuel in that
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situation and it's trying to add more
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fuel
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and it's unable to do so that's going to
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set that code
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related to the fuel pressure being low
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you could have a bad fuel pump
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not putting enough pressure there or
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even a fuel filter that's partially
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plugged up
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not getting enough fuel there or the
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oxygen sensors
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now there's four oxygen sensors on this
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vehicle
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there's two in the front and there's two
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that are further down the exhaust
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the ones in the front are the ones that
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we're concerned with those are the ones
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that are going to
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monitor the engine's fuel air ratio
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so any unburned fuel or air gets into
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the exhaust and that o2 sensor
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will monitor that and send the signal to
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the computer
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and make adjustments well if this o2
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sensor isn't sending the correct signal
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to the computer
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that's going to cause an issue i hope
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this video helps you out
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if you enjoyed it please subscribe to
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