What Does SYSTEM LEAN Mean?
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- čas přidán 4. 04. 2016
- What The Heck Is SYSTEM LEAN? No one likes when the check engine comes on in their car. One of the more common issues with check engine lights is a system lean fault P0171 is the most common fault code. This fault can be tricky to diagnose if you don't understand what system lean really means. This can be too much air, or not enough fuel at the engine. System lean is not hard to diagnose, once you understand it.
Join me today as we discuss:
~One of the most asked questions I get
~Perspeption of unmetered air/not enough fuel
~Calculation based on feedback from sensors
~How does it happen
~O2 sensor voltage
~Correction by ECM
~VCDS Reading
~VCDS Demo ~ • VCDS or Vag-Com Review...
~System Rich VS System Lean
~Diagnose system lean on my Passat ~ • Volkswagen Check Engin...
~and more
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Nice review. For those of us who don't do this every day, remembering which way the values are pointing is the first hurdle. Also it's wise to remember whether we are looking at the correction (fuel trim), or raw O2 sensor data. That's mostly a matter of understanding tools, in this case the interface program we are using. Conveniently, when looking at O2 sensor data, higher voltage means rich, and when looking at trim, higher positive numbers mean the system is adding fuel. That similar alignment makes it easier to remember. Of course on the surface it can be confusing since adding fuel is usually a response to a lean condition downstream, which may be completely corrected by the addition of extra fuel. So I see your point, look at trim first because the O2 sensor data may be obscured by correction of injector pulse width. Thanks! Your description of the most common points of failure adds practical guidance to how experienced techs solve problems.
Nailed it. Been to so many mechanics, had the PCV done, injectors, EVAP, MAF....Paid thousands. Still got the fault code. Had a root round the bay today myself and found and easily found the brake valve hoses were badly cracked!! Just paid $165 bucks for replacement, can't wait to get it in and test it. The cars fuel economy has been terrible for over a year!
please let us know if it worked!
Thank you HumbleMechanic for making this video and your clear explanation. I found my wife's problem through your basic explanation. the last time the Subaru was in the dealership they removed a clamp and never replaced it leaving the air intake the fall off which is what caused the check engine light. I never would have thought to do a visual inspection had I not watched your video. Thank you.
Great video Charles. I remember having a big problem with this on my old 1.8t AWP engine. I replaced the diverter valve because it went bad and when reinstalling the hose on the left side of the diverter valve it was in a slightly different position than it was initially. This caused it to touch what looked to be a metal fuel line behind it. From the heat of the fuel line the rubber hose split open causing a huge leak. I battles this problem for a LONG time and the car always ran in limp mode. Just advice to everyone when working in your car, pay attention to all the details!! Listen to Charles! If i just did a more thorough inspection it would have saved me a lot of time and money. Lesson learned I guess.
Such a great video. You explain things so well! I have one of these in the shop right now and I can't wait to get back tomorrow and figure it out.You really make me want to continue my career as a technician.
Visual inspection… yep, I found the problem and fixed it! Thanks very much Charles for another super-informative video. Keep ‘em coming!
I didn't get that opportunity for visual. I had to feel around the back of the rear most intake hose into the bank 1 throttle body.
Rib
Rib
Gaping hole
Rib
😂
I don’t know much about cars but this video has helped me tremendously in understanding what’s wrong with my car. Thank you
Hey HumbleMechanic, I really enjoy this community of channels, I mean You, EricTCG, ScottyK, ChrisFix, and others, this community has really served me well and saved me 1000's of dollars, i'm getting a new clutch atm, paying 1400 for a shop to do it, a HD clutch in my 2002 3.4L V6 Hilux which to me is reasonable, I cannot do that with my tool kit, just before having to surrender my car to the shop, for the first time ever in 5 years it would not start, I have a new battery, it cranked strongly half a dozen times, cranking it for a handful of seconds each time, it did fire up eventually after letting it rest between each attempt and it was rich, tested all the vacuum lines, they were fine, pulled out my MAF sensor, it was dirty, already had the cleaner and turned out that was the problem, MAF was filthy, easy 20 (for the can Co2) fix that, I can only guess what a shop would charge extra. I asked Eric to recommend more Toyota designated Channels and he did name ScottyK, so I would like to ask you the same Q.
Thanks for the kind words to all of us. It really means a lot. This type of thing aint easy, so it's always so warming to hear. I don't really know many Toyota sites. I wish I did LOL, that is like a foreign language to me HAHA
This is an awesome video Charles. I don't know how many times I've seen people throw o2 sensors at a vehicle with P0171 and 174 without any diag.
Raises hand. I threw o2 at after a $500 valve cover replacement by a "professional shop" and a MAF and still coding. I have an aftermarket INjen cold air intake and Im blaming that because the car run better with it, than without it and it snorts. 2.5L 06 Jetta
Easy to understand that is a gas guzzler nightmare! Great video 👍
very cool charles TIL thanks for the awesome vods
just had this issue, my PCV system had big cracks and vacuum leaks. don't forget to look there also!
You're a great educator my friend
Clear and concise
Thank you
Excellent review, very informative and detailed. Great display of knowledge.
thanks humble mechanic. you are a great inspiration to me and many.
Thanks for the vid Charles! Very informative! I have that intake on my GTI & love it!
Glad to help. Also thanks for the feedback on the intake. It's pretty legit.
This was EXTREMELY helpful.
Excellent presentation....
This video is so perfect. You made me finally understand how all of this works. Great job! My brain always went to vacuum leak in a system lean condition. This gives me much more to think about. Thank you!
great informative video...keep em coming
That Integrated Engineering intake looks awesome!!
Great job on this video!
Very informative! Somehow, I knew exactly what you were talking about. I LOVE cars
💙💋💙💋
Very clear and concise explanation! Helped me finally understand what that damn code means! Lol Excellent video. Thumbs up!
I appreciate the explanation and insight.
Very detailed information thank u sir...
well said explanation on fuel trim percentages
Thank you for the information.
Thanks. Nice explanation
Hey Charls.. keep up the good work. i watch your videos probably 3-4 times to make sure i get everything you say. because there are so much information to absorb as a student mechanic. thanks for all the information (Y) good luck
Thanks so much for the kind words. Glad to be able to help.
Great video!
verrrry good video!! Thanks a million! subscribed!
Thanks so much
Hey Charles, good vid touching a bit on the topic of lean (P0171, P0174) codes focusing on un-metered air and faulty O2's. I Ever give any thought to skewed MAF readings i.e. dirty/ faulty MAF or perhaps issues in the VVT causing lean trouble codes, engine mechanical timing i.e. incorrectly installed timing belt on one cam, sheered key ways etc. or perhaps engine mechanical condition i.e. valve lash etc.? Just curious your thoughts on that and also any thoughts on chasing down lean codes on speed density engines as opposed to MAF engines? Also may keep in mind to that an ignition miss-fire will cause a lean code :) No combustion and all it does is pump air right? HC's can not be read by the O2.
+South Main Auto Repair I have only ran into maybe 2 sys lean caused by mechanical issues. It's sure possible, but not common(in VW land anyway).
I agree that there are more issues with system lean. But I think that will be System Lean 202 class. Haha.
For the first run of these videos I want to keep it simple to get people mind moving in the right direction. Mostly so thy stop just throwing O2 sensors in.
Wait you mean if I get a lean code I shouldn't just change the AFR's and a fuel pump first ;) Haha Can't wait for Lean Codes 202 :) I have had a few neat case studies on mechanical issues setting lean codes... they can mop the floor with ya if you are not careful! Keep up the good work!
+South Main Auto Repair ERIK O FOR PREZZ LOL
South Main Auto Repair Saturno Outlook
Saturno Outlook 2008
First I loved this video, even though I have (knock on wood) never had a P0171 fault code. I suppose I liked it so much because of the training that I had was useful in making sense of the jargon that was used in this video. I don't know what expertise level your user base has but for those who have not had training in fuel systems it may be useful to put definitions in boxes while you are explaining more complicated troubleshooting techniques when using jargon such as fuel trim pulse or width. BTW you it would be cute to get a beard and mustache for our daughter and dress her up as the HumbleMechanic for Halloween.
Cleanest mechanic on youtube for sure. Lmao almost like an infomercial for mechanic tipsz
thanks for good explanation
Man so much good information, great video. Quick question, they did a fuel decarbonation and fuel duct cleaning and my car is back firing at idle and acceleration, is that normal for the first few days?
Thank you sir!
I'm new to VW, and never heard of this condition. I really learned a lot and like your explanations. How do I send individual questions to you?
Great name btw!!
Quick question kind sir.
If i'm planning on replacing my oem header and oem catback exhaust, would that affect how my car will run, lean or rich?
without it being (tuned)
great class
Hey Charles! I like your videos a lot. I have an old 92''s Mk3 Golf with 1.9 turbo diesel engine (AAZ). Do you know any simple mods for these engines? I know one and it is adding an intercooler. Would isolated from engine heat pod filter do any good?
P.S. I hope I wrote everything understandable.
"System Lean" means the car is on it's side. Check for overweight driver or passenger, angry mob, earthquake-related fissure, unusual changes in gravity, or acts of god. Not to be confused with "System Rich," which is when you suddenly find yourself driving a Bentley. :D
Another great video! Love the visual aid. Who ever thought a giant tube could teach so much?
what if your running lean with out being on Wide open throttle? also having lean issues after rev down ..so rev it as it goes down ..runs lean
Please do more videos like this
Thank you sir for this very informative video!
👍🏻 👌🏻 great video
Really feel like I can be a mechanic after watching this 😶😳🥰
no you can't.... what you 'feel' is imagination and very different from actually doing work with tools correctly.
Doug H. in VA shut up Doug 🙄
Doug H. in VA yeah, shut up Doug. 😂
@@DougHinVA no 8
You belong in the kitchen!
I had this on my Toyota 3.4L V6, it was the Mass Air Flow Sensor, cleaning helped, replacing fixed it.
NCIE
How long after you cleaned it did you just decide to replace it ?
You aren't going to have a vacuum leak before the throttle plate. You will however have an air metering error comparing the intake mass air vs O2 reading. The idle air control valve could cause this issue as well being it's a controlled vacuum leak.
I just had this happen on a car I bought, turns out the previous owner must have had an intake kit on the car and then shoved the old standard intake on before I got it and forgot to mention he had somehow sliced a big gash in the underside of the intake pipe causing a massive vacuum leak that I couldn’t see until I removed it.
Can an OBDII diagnostic alone can determine the exact cause of 'system lean' error code?
Also, if the fault is with the oxygen sensor, is it best to replace both (I know there are 4 in a normal car) one before the catalytic sensor and one after? even if the second one is not faulty?
Thank you for the great informative videos. Subscribed!
good video, beardy!
+Don Moore LOL, thank you
I have been dealing with this code for about a month now on my 99 yukon. I have checked and cleaned everything i could. Just found the problem yesterday and it was that the exhaust flange gasket deteriorated away and it is located right before the o2 sensor.
Hey Charles, total of topic question.. i recently watched a vr6 collaboration vid u did a while back which really helped me understand my car, but im having an issue. i got a p1340 on my OBDII so i took it to the mechanic and i was told it was a camshaft position sensor. He told me there wers two of them, but i could only spot one on the right hand side. If you have some intel or advice on how i can find the second one that would be great. thank you
You should do a episode or episodes of pro and cons of doing each mod, and when doing a certain mod, what you should do
Thank you very much Charles for this amazing video.
I have a Chevy Silverado with 4.3 liter engine started missing one night check engine lite came on system lean bank 1 short term 55 long term 25 no vacuum leaks. Suspect a bad 02 sensor before cat and looks like that's what your saying in video. Thanks for showing
Very good explanación thankyou
i replaced my o2 sensor problem i put in crocked because some striped the treads my screen on the 02 sensor screen on the end got crushed and it spines could that cause o2 sensor to fail
Hey Charles, great video by the way.
Broda i have a misfire that starts when the engine is at working temp.
After i downshift at aceleration. Mostly at 2nd and 3rd gear.
Spark plugs are new, cables as well. ( its a Seat leon 1.4 16v axp engine 2002).
The fuel pump resistance gives me 3.5 ohms. According to the info i have seen that it should not be over 3 ohms. So im starting to think that is the fuel pump that when it gets hot dosent reach the minimun pressure. And the mixture gets lean.
What do you think or what would you do for this case.
Thanks a lot, and sorry to disturb.
God bless you.
Your videos are awesome and a great help. I could really use some help here. I have a 2009 Audi A3 2.0 L turbo. My daughter was driving and it just shut off. Before doing so she says it sounded like a diesel but its a gas engine. I towed the car home and began to work. I have since changed injectors, cleaned all the carbon out of the intake manifold, changed the plugs and coils, pcv valve, oil and filter, cleaned the mass air flow sensor, cleaned the throttle body, and various other bits of cleaning along the way. While doing all this over the course of a month I had the battery disconnected. I put everything back together and attempted to start and it cranks really fast but wont run. I am getting the following codes now:
P0016
P0171
P0300
P0301
P0302
P0303
P0304
P0341
P0506
P12A2
Im not sure where to go with this now, could it be a broken timing chain?? Any ideas or suggestions would be greatly appreciated. Thanks.
Hi mate,it’s had a new fuel filter,intercooler.....could have a problem with the maf and not get a check light?Cheers pal luv the channel
best teacher
Prefect vid
Hey Charles any chance of a video on system rich
Great video, I have the P0171 code on my 97 Oldsmobile and on top of that the car doesn't start half the time. I changed the fuel filter like 10k miles ago and the car has 120k miles. I'm thinking since the car doesn't start half the time it might be the Fuel pump. Any Idea if it can be something else. Thanks
Smart guy. Great details. And if I was a mechanic or Am aspiring one, I Might have understood a tiny bit of that. Nope. I watched to see of I could learn how serious this is in the short term....onto the next search result.
It can be minor or major. Totally depends
Hey there
Hopefully you can help me with this I have a Chevy Silverado I have a hard time starting it usually takes 2 to three try for it to turn on and when it does white smokes come out along with gas smell any idea of what can this be?
I have a mk6 gti I just installed a cold air intake and I got code p2177 when I’m driving it seems like the car idle drops just a little while driving .
What would be the cause of a lean condition from using E85 in a non flex fuel vehicle. From what I've gathered for my vehicle, is that it's burning more efficiently or cleaner, or faster. Could it be that my vehicle is not pumping enough of the E85 to be efficient?
Getting a P12A2 at the same time. Cold start misfires first (most likely carbon), warm engine, clear codes then get P0171 and sometimes P12A2. Fuel filter has not been changed for a while
i like this guy, he’s very detailed and knowing what he is saying.
Thank you
bro please answer some of these questions they pertain to others as well
I answered that question on O2 sensors in a reply to the person that asked.
could a code still be stored after torn air intake boot was replaced?
I have saturn ion i put a short ram intake in but there is a secondary air injection hose out and i get a check egine light idk to replace it back to stock or try n remove the hose
So on an MK4 (2001) Jetta (1.8T AWW), how many drive cycles will it take the CEL to reset on its own (After a fix)? I did the stupid thing when I first bought this car (because I wasn't sure I was going to keep the car...) - I bought a $19.00 MAF from ebay. It only lasted 8 months, and then began (even after cleaning) under-reporting airflow, causing an intermittent P0171 code every time the LTFT hit 20% (Under ALL engine loads). Today, I installed a Bosch MAF, and cracked a smile when it entered closed loop, and STFT immediately pegged at -20% while the +20% LTFT began dropping. 3 drive cycles later, I have less than 8% LTFT and still have some negative STFT, which is still working on bringing that LT number down. I'm confident the problem is fixed, but wondered how long it will take the ECU to figure out that the problem is fixed and clear the CEL. Figured I'd ask a VW man :-)
Inspiring
How bout a short in a sensor wire. Could it cause problems with other sensors in the same part of the system?
About a year ago I had some 02 codes on my v6. Ended up replacing all 4 o2 sensors. 6 coils. 1 cat converter and inlet manifold gasket. All good for 6 months now I'm getting bank 1 and 2 lean at idle codes.....
All the long and short trim figures look good.
What could it be ?????
Hi can you guide me a little.
I get a engine lean check light when ever I go above 70km/h or going uphill or even when press hard on accelerator. After turning off engine and then turning back on the check engine light disappears.
What could be the cause?
Would a bad upstream air fuel meter that correcting at 35% drop the correction to almost normal at WOT?
Hey, I have a question. Is it possible that Longtube headers and no catalytics on my 1999 Mustang GT are causing a lean condition? Ive changed alot to stock as i bought it modded. Only thing aftermarket is those headers. Also I will have the PCM Reflashed at ford to the stock flash in case the tuner I used didnt do the job right, just to start with a clean slate. Revving the engine repeatedly makes the fuel trims go down from 25% to 10-17% idling until I leave it idle too long then they rise again.
2 cylinders read bad st autozone.. Changed out coils... All coils going out over time.. 2001 f250. Changed last ones almost, after changed, went to autozone, had system lean and both cylinder reads.. Was not 250 miled yet to reset. Was reading from O2 sensor.. Will a coil issue cause a system lean reading from the 02? My heat is also jacked up.. Am wondering if low coolant levels could cause that. After coils failed, would see smoke coming out of engine.. Looked like a leak somewhete possible but dont know
My 02 ford expedition gives me p0171 and p0174. It turns off on me. I stressed out.
Love the viddeo. New sub
Did u fix problem? If so how?
I have a Vw cc 2017 on a unitronic stage 1+ tune and I want to add a unitronic Air intake but some people say I will be running lean? Is that true ?
Vacuum leaks look for loose and add tape to the male end or cut off the end of the vacuum line that has stretched or replacing the vacuum line.
I have 08 Passat 2.0T 122k miles. CEL is on. P0302 P0171. CEL is on. I changed all sparks/coil. And now the CEL is still on for P0171 system 1 too lean bank 1. But after changing spark/coil. I get a random misfire with the random shaking sound from exhaust then white smoke coming out. Can it be the 02 sensor (downstream) that’s causing my misfire and system to lean?
Would old gas cause this condition? I found my pcv tube that went into the cold air intake loose and barely in creating a vacuum leak. When this happened my idle was rough and stabilitrak light came on. I didnt think I would make it home. My spark plugs were fouled. I cleaned them all and fixed the pcv tube leak with zip ties. I drove the vehicle several days later and it idled fine but my check engine light is now on and it gave me codes p2096 and p2098 lean fuel trims bank 1 and 2. With these codes set is that from the previous issue (vacuum leak) or is this now another issue (possible bad gas)?
Do you have an idea what it means if you just get one code of p12a2
Hi Humble, my 2006 Jettta 2.5 has the tendacy to reve up when stopped or idle, the RPM would rise without my pressing gas. My engine light is on, but still drives. Also my fuel gauge shows empty yet i have gas, drives and fuel light is not on. Please help. I love this car, so i am gonna invest.
Where can you go to view your vehicle's numeric values if you look at it from a Snap-On tablet or the computer things that show all the stuff like at 2:55?
I just changed a coil and all sparkplugs after a misfire issue, it was running good for a few days and now, now I have a system lean code coming up and I’m losing lots of power. Any thoughts?
Spoken very well i truly liked this video cause a code came up on my 94 mustang gt saying running lean. Now i can pin point this problem better, Thank you for your amazing knowledge very awesome.
Thank you
very cool DUDE🙂👍 being a daughter who's DAD was a machines on the railroad GREAT Job GERI KING CALIF
AWESOME and thank you .
Great video. I'm afraid I fall into the diy camp of changing a long list of parts on my 2008 Audi a4 2.0t fsi, and not fixing the problem. I also had it at a local shop that said they did a fuel pressure test and a smoke test, and couldn't find the problem. Not an Audi specialist. Wonder if I need to give up and pay the dealer the 169.00 to diagnose the problem. I changed the MAF, purge valve, checked the hpfp and changed the cam follower even though the one in there looked fine. Changed plugs, Mercedes fuel system cleaner, fuel filter, pcv crack case thing, pcv hoses. After changing the pcv hoses it got better, but still comes back after a long drive (over an hour) and only shows at idle. Lumpy, almost dies but doesn't. Otherwise runs great off idle. I am stumped. Only throws P0171, no other code.
Hi David i done the same as you 2007 Audi A3 1.8T , my engine runs fine , then one day i notice a check engine light , hooked up the scan tool and it was a P0171 , first thing i changed was PVC valve , MAF sensor , air filter , fuel filter , i cleared the code every single time but comes back , buy this time im getting confused , take it to garage they hook up smoke machine they said it was your rear main seal and showed me where the smoke was coming out , so i thought i would try some Rislone rear main seal repair oil and it has stop the slow oil leak i had but the engine light still comes on??? ,
@@karlhendricks8864 Thanks for the comment Karl. It's been fixed for several years now thankfully. The problem was what I will call a breather/vent hose that I believe goes between the crankcase and manifold. On the 2008 2.0, it is a silver metal formed hose toward the front passenger side on the engine. A German mechanic told my mechanic to take it off and blow through it from both ends. Apparently there is a valve in the middle of the hose you can't see that should stop air flowing in one direction. Since the mechanic could blow in both directions it acted like a vacuum leak which usually is far worse at idle since there is little fuel being demanded. A new hose fixed it. Not sure if that crank case vent hose is on the 1.8 or not.
Wow that's good you have it sorted out , and it was just one breather hose ! Maybe I will check mine
What is a good scanner that shows freeze frames and live data for us diy guys to diagnose these readings without breaking the bank?
So with lets say + 25 lean code if 02 was bad would ECM send 02 code also with lean code?
P0171
I would like to add something to this that i just experienced. I have the n249 delete sia delet etc. And this code gave me the run around for weeks. Smoke test leak test everything. Well because of those deletes i have bypassed my diverter vacuum line to the throttle body next to bank 1. Well the vacuum side of the diverter when out and was allowing boost pressure to enter after the trottle body right into bank 1. Long story short. New diverter valve fixed it. Sad part about this is a smoke test wont show it
I have a 2010 cc 2.0t, on new and old maf sensor the same p0101 on idle short trim 25% longtrim 0 for about 2min to 5 min until warms up, then short gets to 4-8 and long 40 - 49 on idle for 3min and on idle stabilized to short trim 0 - 48 long trim. It could be the wires?
Intake No leaks the turbo whistle when driving and missfires p0300 to 0304 and the p0101 codes don't think is the cat plugged but Not sure.
Thank you in advance.
so if my top o2 sensor has 2/3 ripped wires and doesnt work is my engine running rich? my car smells like a diesel sometimes lol 2016 dodge dart