P0171 Trouble Code: System Too Lean Bank 1 Diagnosis

In this video, I show you how I troubleshoot a Check Engine Light (CEL) / Diagnostic Trouble Code (DTC) P0171, System Too Lean Bank 1. The exact vehicle in video is a 2002 Toyota Tacoma standard cab 4 cylinder pickup truck. The techniques shown can be used on many vehicles, not just Toyotas.
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Due to factors beyond the control of the Big Dog50001 Automotive Channel, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. The Big Dog50001 Automotive Channel assumes no liability for property damage or injury incurred as a result of any of the information contained in this video.
The Big Dog50001 Automotive Channel recommends safe practices when working with power tools, in on or around automobiles or other vehicles, automotive lifts, lifting tools, jack stands, electrical equipment, automotive modules and systems, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video.
Due to factors beyond the control of the Big Dog50001 Automotive Channel, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not the Big Dog50001 Automotive Channel.

[@tonyfox1434]

I watch and learn diagnostic trouble codes daily and to be honest, your way of using a cheap code reader with live data was the most interesting and informative video I have seen in a long time. Thank you, and all on a cheap device !!

[@m2svirtual384]

It would be impossible to add up all the hours of auto repair videos I've watched over the last 8-10 years. THIS ONE, though, MAN!! In only 46 mins... I'm speechless at how easily I absorbed every concept and it made logical sense. I was starting to diagnose ahead of you! You sir, not only have a gift of mechanics and troubleshooting, you have an even greater gift of TEACHER. Never boring, just a concise step-by-step stream of logical information. I stood at a standing ovation at the end of this video, and I cannot thank you enough for the education you imparted upon me. Thanks Dawg!

[@john3tim]

Could not have said it better. Very clear and logical.

[@likits1999]

I agree. It was like being in a classroom with an great instructor.

[@dennissalisbury496]

Me too!

[@coleimhuelsen]

Agreed

[@michaelpigeon3591]

That was one the best and formative Video I’ve ever watched. Thank you 45:52

[@SDMev1982]

Some of the best 46 minutes I’ve ever spent.

[@BigDog50001]

Thank you, I appreciate the comment!

[@sandiego7625]

0

[@cal48koho]

hard to overstate how sharp this guy is. Beautiful explanation . This is at a high level expert mechanic level!

[@keninswed]

Totally agree man knows his craft. He is not a change this item kind of mechanic but a motor doc.

[@stupagia26]

i don't normally respond to videos, but I almost felt like this gentleman was standing next to me and showing me all this in person and not shouting at me. Best of all is I appreciated how he explained everything he was looking at and what significance it had in terms I could easily follow along with. Turns out he lives in my neck o' the woods. Thanks Big Dog! I promise I won't tell, Scotty! :{>

[@michaelpigeon3591]

Agreed

[@billlincoln6087]

THE BEST MAF DIAGNOSTICS ON THE INTERNET.

[@BigDog50001]

Thank you for the comment!

[@Sheeeeeeeeeeeeiiitt]

I agree! He does an excellent job communicating in such a way that his message doesn’t get lost in translation. Very informative, relevant and concise. Thanks for sharing the content Big Dog50001 Automotive.

[@thomasrouse9146]

0a

[@NoneFB]

@@BigDog50001 I wonder how much that Vantage is....

[@princekodeys3028]

000000

[@robertlardon3782]

The most thorough and insightful "how-to diagnostic" car video I've seen! The 46 mins went fast with no fluff; just great information. Big Dog is a great mechanic and teacher!

[@BigDog50001]

I appreciate the comment, thank you!

[@evandrewmartinez1]

This video made me feel like I already fixed my po171 and I haven't even went outside yet

[@BigDog50001]

lol

[@jrnycg3589]

😂😂

[@randallmcclain6368]

Lol I know what you mean..

[@dougsanders6034]

Great informative VIDEO! I have found that EGR valves , PCV valves , and IAC valves are notorious for sources of vacuum leaks.

[@juancortez2067]

Off

[@michaelclayton4703]

As a driveability expert myself, you did an absolute awesome job, for not only a layman, but also experienced technicians! I am not ashamed to say I picked up a few tips too! Outstanding!

[@BigDog50001]

Awesome, I appreciate the comment, thanks!

[@netwonc]

The very best analysis of this problem. Shows how to test all systems. Thanks for sharing your knowledge with us.

[@BigDog50001]

Thank you for the comment, I really appreciate it!

[@user-sq8rs2lc9c]

THE MOST DETAIL DIAGNOSTICS PROCEDURE PRESENTED IN THIS CASE STUDY. SO BENIFICAL AND ACCURATE. THROUGH DIAGNOSTICS 1) VACUUM LEAK 2) BAD MAF 3) BAD BRAKE BOOSTER. ALL 3 STEPS ARE SUPPOERTED WITH STFT AND LTFT. JUST PERFECT WORK.

[@ashercohen4739]

First of all, thanks for the video, I'm trying to understand the fuel and air problem, it's not easy, but now I've learned something else, it's 85% of vehicle problems, thanks again

[@spiketaterman5181]

Thanks for this! Was driving my car over rough roads, and the check engine light came on. It threw a P0171 code. Once home, I popped the hood and saw this plastic chamber thing had fallen off the air intake throat pipe DOWNSTREAM from the MAF sensor. Popped it back on and tightened clamp with a screwdriver and good to go! I love youtube university...

[@BigDog50001]

Good to hear you got it fixed! Thank you for the comment!

[@ericjernigan655]

Hands down the best diagnostic video I've ever watched on KZbin (and I've watched a ton). I learned more in that 46 minute video than all the others combined. Outstanding teaching video.

[@joelbarndt6907]

Great vid! You just saved me from taking my car to the repair shop. Read the code and had a closer look at the hoses. Plain as day one hose had come loose. Thank you!

[@BigDog50001]

Glad it helped, thanks for the comment!

[@retiredsoon1365]

Had a similar problem on my old Toyota Yaris. using an a very basic analyser fault codes only. I followed your advise and found a damaged air line going to the throat of the Mass airflow. Replaced with a generic hose now idle is restored and my old car lives to fight another day. Thank you for your video.

[@erobbinstube]

I came here trying to track down a P0171 code on a 2003 Toyota Corolla, and while I think my problem is due to a leak at the intake manifold, I was floored by the quality of this video. I work in the high tech field and work on troubleshooting issues on a daily basis. This video is a text book example of the method needed to properly come to understand the root issue of a problem. Outstanding video.

[@BigDog50001]

I really appreciate the comment, thank you!

[@johnnyloveee]

Same. I'm gonna have all of this knowledge tomorrow. Thanks man. This is amazing.

[@teemackin89]

I’m going ins

[@seanmcguirk5808]

I agree. Really well done.

[@mech4061]

Ed Robbins. I too and getting ready to work on a 2003 Toyota Corolla with a po171 but mine is combined with a po125. It could be a stuck open thermostat or a faulty coolant temperature sensor or something with the wiring on the po125 Not sure what I'll be getting myself into on this one but I believe the po125 could be causing the po171 which is a lean condition.

[@rubbermalet9292]

this is actually "prime time info" bro im a retired mechanic with many years in the industry - i still practice with neigbs & friends' cars lol- and the way you'd explain everything regarding this issue is basically the same way automobile instructors do at automechanic schools & at college level too, very professionaly w/o any gimicks thank you for taking this time and to help us to understand the technicalities involved within 💖

[@BigDog50001]

Thank you for the comment, I really appreciate it!

[@ivaneatoniii5025]

I totally agree, I work on my own autos, and my family as well. I am a Grad of T-Ten for Lexus and Toyota. I am not working in the field anymore. I make more money with my current path. That being said. My Instructors should be made to sit with you. So they can teach the new guys correct ways to learn diagnostics and breaking down the steps. I say that because I was dumbfounded when in the middle of a class on Finding a obvious fuel delivery issue. The instructor refused to even entertain a possible pirate air issue. While he set it up to be fuel issue from a under pressure of fuel being delivered. You should always go simple/Cheaper/faster diagnostics before you go to harder issues. pulling a vacuum test on a fuel rail is a little harder then watching fuel trims and alteast checking off not pirate. Great job. Also I disagree with only one of Rubber malets comments. You know you trained that damn fly.. It was a gimick fly!!!

[@stealthg35infiniti94]

Thank you very much for helping fix my car. First it started with a P0420 Catalytic efficiency code. Then graduated to a P0171 lean code. Your method of explaining Fuel Trims issues and MAF Sensor testing was the Key to determining a vacuum leak. Then I looked at all hoses and used Brake Cleaner still couldn't find the leak. Finally after a quick prayer, I remembered, don't forget the brake Booster and PVC valve. Sure enough, I pinched the PVC hose to the intake manifold and the short trim fuel went from Maximum to Zero in bank 2. Bank 1 went from Maximum to about 3. Tomorrow I'm installing a new PVC valve.

[@BigDog50001]

👍

[@quintingooing5495]

This video was the single best KZbin tutorial I’ve ever seen

[@BigDog50001]

I appreciate that, thanks!

[@mikeb7887]

This video is one of the best full explanations of the diag process I have seen. Really well done and very clear to understand. You tied in fuel trim, scan tool, O2"s, vacuum gauge, and scope to clearly show us what is going on with this engine. Thank you! Mike B Tarrytown

[@BigDog50001]

I appreciate the comment, thanks!

[@raygooding9935]

@@BigDog50001 this video has inspired me to become a mechanic. Good job bro. Thanks

[@darrinfaulkner8911]

I sat and watch this whole video on my 1 hour lunch break and must say this mechanic is like a school teacher that was teaching myself the student.Great video and he was very articulate and professional in narrowing down the problem.The explaining of the OB2 reader was on point as well because I use mines alot but dont understand some of the word play on the tool until you explained it.Thumbs up to your video👍...

[@BigDog50001]

Glad it was helpful, thank you for the comment!

[@josetovar9222]

Your video just saved me hundreds of dollars! You’re THE man! What a great teacher!

[@BigDog50001]

Thanks for the comment 👍!

[@davechambers5279]

This is a simple fix. I learned the hard way. I popped code P0171 and then I also popped P0174. Thinking I need to do all these things; changed plugs, coils, MAF, ran smoke machine and no vacuum leaks, and changed the oil and filter. The messages said my fuel injectors were bad or needed cleaned. I dumbed some Seafoam in my tank but did more research before driving my truck around. Well, I spent $5 and bought a new PCV valve. The old one did not rattle when I shook it telling me it was clogged with sludge or just no good. Popped the new one in which did rattle, started my truck and all codes were cleared and truck runs perfectly. Try the PCV Valve first.

[@alia176]

This was an EXCELLENT video, good job Dave. You're a good speaker and a camera operator. You dumbed down how an ECU manages the engine to a level that I think most of us will grasp easily. Your steps are logical and easy to follow. Thanks for taking the time to make this video.

[@BigDog50001]

Thanks 👍!

[@candicekillmer4694]

This video helped more than any other video I've watched trying to figure out how to fix the p0171 code. And I'll be dammed if it isn't a freaking brake booster leak. We have Been trying to find this vacuum leak for 3 months and couldn't find anything. Replaced many parts trying to fix /find the vacuum leak. A lot of money into repairs that weren't needed and a waste of money. Thank you for going through every possible reason to get this code. This car was pissing me off and I've become more of a mechanic than I ever wanted to be. You just saved my scion tc from going to the scrap yard. Thank you!

[@BigDog50001]

👍

[@darrinfaulkner8911]

You sound like me with my car and all these repairs I've done and it was my booster.No regrets though because the market value on my car went up and I've became a better mechanic that saved money for future repairs at rip off mechanic shops...

[@tedcarlton9905]

this guy really understands how it works and how to use the tools plus he explains things in clear way

[@BigDog50001]

I appreciate the comment, thanks!

[@LaylaSlays_always]

I don't think anyone could explain how to diagnos a lean condition better than BigDog50001 did in this video! Great job, and I truely gained a huge amount of knowledge, thanks so much!

[@wendwllhickey6426]

I had same po 171 and it turned to be a maf sensor had only 1.2 ohms and need to be 2.5 to 3.5 ohms on sensor change out sensor fixed it

[@nothingspecial6248]

Qa

[@richardr5774]

This is a great teacher! I now understand fuel trims, something that was a mystery to me even after watching hours and hours of "SMA" ! Thank you , Big Dog , for making it so easy to understand, I"m now a subscriber !

[@BigDog50001]

SMA is awesome. Thanks for the comment, I appreciate it!

[@1guardia]

I totally agree. Well explain!

[@studhammer]

Wow! This was the most educational video I’ve ever seen. I just got the same error code on my Camry and this video shows me how to troubleshoot. You sir are an incredible teacher!

[@BigDog50001]

I appreciate the comment, thanks!

[@MrBlueWRX]

Probably the best diagnostic video i have ever watched, thankyou.

[@BigDog50001]

I appreciate the comment, thanks!

[@lloyd-qt1mg]

The BEST use of 45 minutes of my life . WOW .... Mr. Big Dog , I'm 'blown away' by your super clear concise explanation! I'm a fan for life...

[@BigDog50001]

I appreciate the comment, thank you!

[@lloyd-qt1mg]

@@BigDog50001 My pleasure. Can't go far wrong with an Autel AL319, as a DIY'er!

[@p52457]

Holy Cow! Change your name. "Big Dog" sounds like some beer drinking bully. I suggest "Einstein Auto" because you are a smart cookie that deserves all the accolades that you have received. Honestly, I have never seen a better video on auto repair.

[@BigDog50001]

lol, good one! Thanks for the comment, I appreciate it!

[@granitecowboy2199]

I have been through a bachelors program in automotive technology and worked the last 6 years on heavy diesel trucks, and this was by far the best of showing how to use FT to diagnose vacuum leaks. Thanks for the education.

[@Borealis2007]

You set the bar so high for the average uneducated mechanic who will have you replace part after part to fix an elusive problem.

[@BigDog50001]

Thank you for the comment, I appreciate it!

[@weldingjunkie]

Most of the time when the pcm is dumping fuel in like that it’s an air problem and visa versa.

[@randallmcclain6368]

I'm guilty of throwing parts at the car I have now but I've been working on old American cars my whole life and now at 40 I'm looking for chokes and floats, points, condensers, caps and rotors and I'm like omg...where the hell have I been? And where the hell did they go?

[@swilson317]

I have a 2002 Miata. Multiple mechanics have replaced parts and smoke tested. We just replaced the injectors! Unfortunately, It’s still throwing the P071! Argh!

[@1guardia]

Is there a way to give you 10,000 likes ?👍

[@AirmanJH]

Very thankful for your explanation of the data. Lots of videos out there about vacuum leaks, but this is the first I’ve seen that explains what all those numbers mean and how to use that info. Much appreciated!

[@Zoomydoomy]

I'm glad I watched this entire video instead of clicking away early on. I learned so much.

[@BigDog50001]

Glad it helped, thanks for the comment!

[@elfocker]

Me too 🤣 awesome work 👍

[@tinapalmisano7554]

Absolutely love your video! Cannot explain how much this will help me. Actually understanding step by step the information under those codes, is priceless!

[@BigDog50001]

I appreciate the comment, thank you!

[@BigAlWillis]

I've watched many car repair videos over the years. This one ranks up there with the very best. excellent!

[@BigDog50001]

Thank you for the comment, I appreciate it!

[@1guardia]

This guy is the best!!

[@JackMeyHoffer562]

I was searching for another issue and found this video. Thanks for the tip on cleaning the MAF sensor. I had this same code for quite some time so I finally decided on the basic and changed all my sparkplugs. That did the trick to get rid of the code. It was probably dumb luck. Thanks again for the quality of instruction in this video!

[@drabusharr]

Superb - watched so many error code videos and THIS IS IT for the P0171 code (and so much more) You have provided exceptional information and methodical trouble shooting that is completely absent in most of todays garages and most certainly a dealers shop. Thank you for making this!

[@martinguitarhd28]

Wow what an excellent explanation on a lean condition.every thing you did and said was so easily understood .Loved the way you went through each detail and use of the vacuume gauge in trouble shooting.Thank you so much for your time and explanation .Really appreciated.

[@BigDog50001]

Glad you appreciated the work, thanks for the comment!

[@sjp3042]

Thank you for being so thorough and sharing your knowledge. You are definitely installing a lot of confidence in us weekend mechanics that like to work on our own cars!

[@BigDog50001]

👍

[@rafaelmeneses5066]

By far the best video that walks through an actual problem while explaining the prices of fuel trims. I have a very similar problem which I feel confident that I can narrow down more quickly with your explanations throughout the video. Thanks a bunch.

[@ccrobinpeg]

Came across this channel by accident while surfing youtube on my smart TV. "Diagnosis" sucked me in. I'm a retired elect tech, computer geek, self-schooled mechanic, ham, engine builder, etc. Watching the step by step trouble -shooting process kept me glued to the screen. I learned what some of those scanner screen displays meant and their interactions. Congrats on the clear explanations of each branch of the TB tree. Learned a lot! Thanks!!

[@BigDog50001]

Thank you, I appreciate the comment!

[@fernandorios8499]

Jesus I’m impressed what a good quality video! I’ve never been so immersed with information! So detailed and specific you can tell he was born to be a great mechanic!

[@BigDog50001]

Wow, thank you!

[@phamster18]

learned so much , from how to know , to fixing and using your experience and showing the results. your data driven fix was so perfect to watch.. didn't waste 40 mins watch, invested in 40 mins for life time problem solving techniques... keep up this great work

[@BigDog50001]

Glad it was helpful, thank you for the comment!

[@chiya2006]

This diagnostic is very precious to everyone. I learned hard way by changing complete ignition coils & spark plugs just to find out that the problem was purge valve and gas cap which I changed later, made the car running again. Yes I suspect I have to go after in details just like what you outlined here as I know I still have issues with either a vacuum leak, sensor problem, maf problem or fuel filter/pump. Thank you so much for taking from your previous time to give us most needed info . Thank you 🙏

[@rockfangd]

I Cannot thank you enough for posting this video. It is the best informative video I have seen for proper diagnostics of the P0171. I have no idea why someone would dislike this. Thank you for taking the time to educate.

[@BigDog50001]

Thank you, I appreciate the comment!

[@joeabs4844]

Great diagnostics and explanation Sir. Your the best in troubleshooting issues here in KZbin! Keep it up!

[@BigDog50001]

Thank you, I appreciate the comment!

[@uno25]

Big Dog50001 Automotive is by far best in class. Who has a more authentic delivery and a nak for delivering relevant content that's easy to digest? I'll wait.

[@BigDog50001]

I appreciate the comment, thank you!

[@2002boriszhang]

I want to thank you for posting this very detailed diagnosis video. I have a 06 Accord with a pending CEL code P0171. Fuel trim was at +25% at warm idle. I followed your procedure, and found out that my air intake tube had 2 huge cracks. After installing the new tube, fuel trim wasn’t changed. I moved on to see the live data and found out my MAF sensor was under reporting. Since the Tacoma in your video and my Accord all have the same size engine, 2.4L, I found my MAF was under reporting even worse than the Tacoma in this video. I ordered a new MAF sensor and now the problem is solved! Thank you again sir as p0171 can be very tricky and costly to diagnose. Your video is extremely helpful and saved me a lot of money. As a DIYer myself, these videos really help!

[@BigDog50001]

👍

[@dougsanders6034]

Thanks (Big Dog), you have probably saved a lot of clunkers from the scrap yard.

[@toneytoney822]

I didn't watch video to the end initially, I had to give you a 2 thumbs up for giving that fly warning! You really broke it down that a dummy would understand. Once again great job

[@BigDog50001]

lol, thanks for the comment!

[@JonathanLHaasw]

Thank you for making it clear how to understand short and long term fuel trim!! I have watched a lot of videos and friends trying to explain this. NOW it’s very clear!! Can’t thank you enough.

[@yasharpartovi5422]

That’s why this video got over 2M view! Mannnn, best explanation I’ve ever seen in my life. technical, precise and practical. I didn’t feel like I’m watching this video for 46 minutes lol. Thank you so much for the video, well done. I think you deserve more. Again thank you for the video.

[@ianmega9550]

You have an incredible body of knowledge in your head... just listening I learned a lot, but I sure have a lot more to learn! Really excellent job!

[@BigDog50001]

Thank you, I appreciate the comment!

[@observer-3861]

What a great presentation! Thank you so much for spending your time to explain the source of the problem.

[@BigDog50001]

Thank you, I appreciate the comment!

[@mikeroberts5646]

Congrats this guy just showed you how not to throw parts on a car without confirmation,this is as good as it gets

[@BigDog50001]

👍

[@mcgruff28]

This has to be one of the BEST videos and most thorough explanations of this info I have found. This guy is an excellent teacher and I wish more people would go into more detail on topics like this so you can see the whole process and not a small sliver of info that wont get you an answer. I got a whole lot of info and this helped me to be able to know what to look for with my issues im trying to fix right now. THANK YOU!!!👍👍👍👍

[@davidholzbaugh652]

Great info ! Your a great teacher!!! We need more real people like you in this world !! God bless you !!!🤙

[@BigDog50001]

I appreciate the comment, thank you!

[@jimintaos]

Thank you, I really found this helpful. I've been working on my 2001 4 Runner and replaced plug wires and plugs, cleaned and rebuilt all of the injectors, eliminated all of the vacuum leaks and replaced a defective fuel pressure regulator and then, yesterday, I bit the bullet and replaced the fuel pump because all of my tests seemed to indicate a fuel pump issue. Still, the same problem. Idles like a champ, maybe a slight miss, but the moment the throttle opens up it bogs down. After watching your video I decided to go back to square one and do what I had done on day one and start with the MAF and work my way back. This time I happened to look into the MAF and saw that the sensor deep down in the guts of it was all crudded up. I flushed it with MAF cleaner, let it dry, put it back, started the engine, blipped the throttle and the problem was solved. No more P0300 and no P0171. Runs like it is supposed to. Only one thing left-the oil change. So, thanks again for the pointers and the process and above and beyond all of that-explaining in a clear, straight forward way without even the barest hint of over amped ego or sarcasm. Consider me subscribed to your channel and un subbed from that other guy. Thanks.

[@BigDog50001]

Thanks for the comment and welcome!

[@jerryhanson3903]

I have the same problem with a 3.8 GM engine. I changed the fuel pump, mass air flow sensor, fuel pressure regulator, vacuum hoses and even the fuel filter same problem. No shop I go to can figure it out.

[@garyzuckerman768]

Mr Big Dog 50001 you sir are an EXCELLENT Teacher. You provide a clear pathway for understanding how to solve at least this diagnostic issue. I know you would take the same effort and then provide very clear communication for any other issue you were looking at and then teaching other about... super job!

[@BigDog50001]

Thank you, I appreciate the comment!

[@drjoeset]

WOW ..... It would have never crossed my mind that the brake booster would have gone bad .... Thank you for the knowledge you bring to the table...

[@dragosb2165]

This is the most comprehensive video I have seen so far. Thank you.

[@BigDog50001]

Wow, thanks!

[@Longtrailside]

Very well done. I appreciate all the hard work that you put into this, it was very educational.

[@BigDog50001]

Thank you, I appreciate the comment!

[@nissanzamyadtech.4856]

Really very Great Video . I always watch this video again and again Because this is the video that helped me to master the the code P0171 code and Understand the fuel trims. Any one who wants to be a true car Diagnostic guru. He must learn the fuel trims and this is the video where you learn your basics. Thanks Big dog

[@matthewmase3549]

this was an awesome video. im a diesel mechanic and couldnt quite understand the percentages on my scan tool when hooked up to something. thank you for your time and this video taught me a lot and is sending me in the right direction for the future.

[@billyyoder8171]

Thank you Dave. Text book explanation. Good job. I appreciate your videos. Have a blessed and safe week.

[@BigDog50001]

Thanks, I appreciate the comment!

[@willefixit]

@@BigDog50001 better than text book!!

[@petmim3583]

The best video i ever watched!! Totally understandable and as *evandrewmartinez1* said "This video made me feel like I already fixed my po171 and I haven't even went outside yet"!!!!

[@BigDog50001]

lol, thanks for the comment!

[@lexathelexus109]

this is single-handedly the greatest diag video i’ve ever watched on youtube, i’ve never learned this much from a video like this before

[@justinmiller3114]

I wanted to leave a comment saying "thank you" for making this video available on youtube. Recently experienced p0171 on my dodge magnum and your information helped my pinpoint my issue with ease. Thank you again from Texas.

[@BigDog50001]

Glad the video helped, thanks for the comment!

[@msb919]

This was very educating and the best I have seen on KZbin! Thanks alot!

[@nfarnell1]

Had this problem with my 3.0 duratec, and using my 319l, went through everything and concluded the MAS was my problem. Installed a new one and both fuel trims came down, after about 30 miles both were at zero with a little up and down. The engine was clearly running better, thanks for taking the time to share your knowledge.

[@BigDog50001]

👍

[@oscarv473]

Oh lord I just finished watching this MASTER CLASS thank you so much please keep educating us newcomers and may the Lord bless me with your wisdom one day

[@DJ-yl5xp]

This video was as clear as it could ever be. Followed closely, concluded that it had to be a vacuum leak to both cylinders (p071 and p074 on 03 avalon). After spraying carb cleaner to no avail ,rubbed my fingers like shown in video along bottom of vacuum hoses and found a crack below hose going to brake booster. Love !!! this dude. 5 stars

[@BigDog50001]

👍

[@jamesoberg8809]

Amazing thorough explanation of diagnosing the problem and a huge help understanding how to read my Autel Scanner! Thank you so much!

[@BigDog50001]

Glad it helped, thanks for the comment!

[@justasmarkevicius2568]

I think its the best and most detailed diagnostics on this particular problem. Good job sir !

[@BigDog50001]

Thank you!

[@jordanarmstrong8358]

I wish all mechanics went as in depth as you did to solve the issue. Well done, sir.

[@BigDog50001]

Thank you!

[@GorillaCookies]

This was the best tutorial Ive ever seen on KZbin. I shows the functionality and correct use of the OBD 2 scan tool. And the way it can be used to eliminate as well as nominate possible causes of error code alerts . Both by monitoring of specific parts through real time performance readings of sensors and overall understanding of each reading and what each one means

[@BigDog50001]

👍

[@user-op1dc6qf9c]

WATCH THIS VIDEO - it's long, but worth it! Very educational. He mentions that if the fuel enrichment goes down as you rev away from idle, chances are it's a vacuum leak, especially on a hot engine. On a cold engine could also be an intake manifold gasket. Watch the whole video. I was able to find an intake boot/duct/joint near the throttle body on a 2006 Grand Vitara. I had missed it before!

[@BigDog50001]

👍

[@patrickthomas6170]

Wow,! As a nonprofessional mechanic and having watched 100s of car videos , you have made clear so many things that I didn’t really understand. Thank you for such a perfect delivery of this content for a regular guy just trying to fix his own crap and save money.

[@BigDog50001]

Glad it was helpful, thanks for watching!

[@toneytoney822]

Anyone that gave you a thumbs down, don't have a basic understanding of 101 automotive. Very informative good job sir!!!

[@BigDog50001]

👍

[@richardjones3112]

What a brilliant explanation.I’m going to watch this at least once a week until it sticks in my cluttered brain! Thanks so much.

[@patriot2164]

Sir , 1st Time Viewing your channel, I love the explanations , I watch numerous automotive channels and alot of those channels seem to think everyone has the same knowledge levels , I love the background information to get everyone on the same page ! Thanks

[@BigDog50001]

Glad it helped, thanks for the comment!

[@patriciomunoz2830]

Hey good video, it's nice to see troubleshooting in 90's cars, every other channel are fixing newer cars Subscribed

[@BigDog50001]

Welcome and thanks for the comment!

[@pidzi31]

This was the best Vacuum leak tutorial ever..

[@nasirjan6903]

This is the best mechanic I have ever seen. You are a scientific mechanic. I wish you were close so that I could bring my dodge avenger to you. It has similar issues but no mechanic can make the right diagnosis. They have charged me more than 10 times but still my car dies randomly while driving.

[@evan937]

My 2000 Corolla had a p0171 for years. I tried replacing the o2 sensors, cleaning the maf and throttle body, gas cap, pcv valve, even checked for vacuum leaks. Finally it went away for good once I replaced the rusted out fuel filler neck. This specific code is a tough one to figure out usually. I love my old Toyota. She has 225,000 km and still runs strong. Sadly I live in Ontario so the Rust is eating her alive.

[@BigDog50001]

Thanks for the input!

[@eseybold1]

Absolutely top quality video - easy to follow and clear - great job !

[@BigDog50001]

Thanks!

[@thomasderrico1751]

As a new viewer to your videos I have to say, as a shade tree mechanic for 60 yrs and raked them damm leaves, I would like to thank you for the best troubleshooting video on the YT. Clear info with the related factors that most other guys and gals leave out, followed through and then checked the results. Thank you brother Excellent

[@BigDog50001]

I appreciate the comment, thank you!

[@johncarlson8986]

Thanks so very much for this video and your presentation. My PO171 code was confusing me mostly because I didn't know what numbers and quantity I should be reading. I followed your steps and upon inspection found a vacuum hose that had not been properly reconnected under the air plenium on top of the engine and a loose cracked brake booster tubing not replaced and clamped by the Garage. I fixed both and the numbers " dropped like a rock" and corrected after some driving. No codes. Now to get the cruise control to work everytime not intermittingly. Thanks again. I will be following you for more tinstruction.

[@bezaleeluk3696]

thanks for the excellent explanation of short and long term fuel trim... now it all makes sense :)

[@BigDog50001]

Glad it was helpful!

[@ronaldmobley4895]

@@BigDog50001 my car runs fine when im driving, but startles a bit at stop lights. My code read p0710. Im stumped because my gas gauge fluctuates

[@robertbcurry2698]

This was great! Very informative and helpful. Thank you for the time you have put into this and the information you shared. I learned quite a bit, just a shame I don't have all those fancy tools you do ;)

[@charlieparson5176]

You've explained this better than anyone I've ever listened to on the internet. Great video 👍!

[@BigDog50001]

I appreciate the comment, thank you!

[@tmph1814]

This is the most educational and useful diagnosis I've encountered to use to fix my 99 Lexus RX300 with a dozen of CEL codes. Thank you very much BigDog!

[@BigDog50001]

I appreciate the comment, thanks!

[@yvonnadeau2331]

I've watch many online auto repair clips and by far yours is the best and deserve my subscription. I have been waiting for you sir. Can't wait for what's next. Thank You

[@BigDog50001]

Thanks for the comment, I appreciate it!

[@bwwilson1765]

Fantastic video! What a great refresher for my very old diagnostic skills. I was looking for just this kind of in depth explanation, as I am helping my son diagnose his dual 0171 &0174 codes on his "new" '02 Ranger with a 4.0L. Perfect primer for the work! Thank you for sharing your time and diagnostic approach in a clear and concise way. BTW, the link for the Amazon link for the MS906BT goes to the MV108 Inspection scope, not the Scan tool, FYI.

[@BigDog50001]

I appreciate the comment and the heads up on the wrong link, thanks!

[@rytoniowendolini2793]

I have the exact same codes together right now as your son, what ended up being the problem?

[@bwwilson1765]

@@rytoniowendolini2793 The fuel pump/pressure was one issue. I think there was an issue with one of the O2 sensors as well I think.

[@kenvitale6118]

I read other comments and am in agreement with M2S Virtual comment. This is the best video I have seen. It gives me confidence in questioning several mechanics have paid to NOT properly diagnose and definitely have not fixed my P0171 issue.

[@BigDog50001]

👍

[@pfsantos007]

Best video on the subject of vacuum leaks. Excellent explanation and very detailed going through the different symptoms and how the readings change.

[@BigDog50001]

I appreciate the comment, thanks!

[@billdavison2303]

Great video for diagnosis of a P0171! Thank you!

[@BigDog50001]

Thanks!