I came back to refresh my knowledge on fuel trims and I don't think there is a clearer explanation on youtube. You are an incredible teacher! Thanks for sharing your knowledge!

47 years in this business, I'm a tuner, a very experienced technician, and I'm at least a hundred training courses in on engine management. This course is an excellent training course in the operation of the fuel trim system. I actually didn't learn new things but again, nobody is born with this knowledge. I'm sending my technicians a link to this video because I cannot see into their heads and know exactly how much of an understanding that they have about this subject. I liked the way that Dan stayed away from brand differences, particular engine differences, and other variables and concentrated solely on the fuel trim system in general. Great job! I highly appreciate you giving this knowledge to bring technicians up to speed on these systems that have been in place for over thirty years and are in use on almost every vehicle on the road today.

It never ceases to amaze me why people like you go out their way to share so much of their knowledge and help people in the way you do. Thank you for your wisdom my friend, it's very much appreciated! :-)

I came out of heavy diesel and construction equipment repair and decided to go into automotive..much of the principles are the same but I wanted to become more familiar with automotive drivability diagnostics...I started watching your channel and bought your book and you really know how to put things into perspective. just from watching your channel and studying your book it helped a lot and let me take what I already knew as it pertained to 15L cat diesels and apply with to the automotive industry..great stuff man thanks a lot

Scanner Danner you make your lectures so interesting, wish my lecturers had been like you when I was at college, had to watch fuel trims two or three times before I could grasp it though, not your fault I'm nearly 64. Ray from the UK.

This video has finally gotten fuel trims through my thick head. Thanks!

great suggestion, I'll put it on my list of things to do for sure. I'm working on releasing the entire book in this format. It will be over 50 hours of material. I'll keep everyone posted when it is done.

@scannerdanner my wife and I both have older vehicles that I maintain and fix myself. Your videos are incredibly helpful to me in my constant battle to turn the check engine lights off for vehicle inspections. Just wanted to say thank you.

you are a real asset of KZfaq's community Danner, thank you for inspiring all of us Auto Mechanics to continue the job with knowledge and confidence

Hands down best technician online period. Thanks for the hard work and dedication for helping others. Im 25 working for police departments fleet in MS almost 2 years in(mostly maintainace and not a whole lot of diagnosis) and im taking online classes. Hopefully one day I'll be half as good as you. First step is to keep watching your videos

ScannerDanner You really do an amazing job. I myself am Master ASE Certified, and as we all know sometimes we neglect to K.I.S.S, which was my case today with a 98 Saturn 1.9l. Came in, no check engine light, rough idle, bad gas mileage, etc. STFT was @ -25% to -30% and LTFT was @ +9.4%. Realizing it was running rich based on the STFT values, I went ahead and pulled the booster vacuum hose to create an artificial LEAN condition. STFT didn't change, nor did LTFT. I thought, hmm. I checked Fuel Press, spark, etc. O2 upstream was moving accordingly high/low, so I was scratching my head for a bit. I watched this video as a refresher, and as soon as you said "reset the ECM for a relearn" that little light bulb went off, and the "DOH" moment arose. I did exactly that and a 3 key cycle test drive for a relearn, and bingo, my values are now back in spec. Looks like the previous shop replaced the vacuum booster line, and neglected to clear and relearn. Keep up the great work man!

Scanner Dan you are the man! I'm 21, just got both my Verus certifications not to long ago and am about to graduate with an associate in Automotive Technology. Excellent lecture! I got more out of your lecture on ST/LTFT than I did with both my basic and advanced Fuel Systems class! Love it when you use the Verus as well as incorporating real world problems and fixes into your videos. If only every automotive teacher had the intellectual knowledge you brind to the drawing board. (pun intended:)

Thank you very much for the comment and book purchase! And I will keep the videos coming.

ScannerDanner, I must say IMHO you're an excellent teacher. You teach the theory, then show it in the field with expected outcomes which helps the student to reason what he has been told. Not only that, you ask questions along the way to see if the students are understanding what are you saying. Someone could say it's pretty obvious what I'm saying, but I've known A LOT of teachers that lack this kind of pedagogical way of teaching.Not only that, you're showing all of this by free. THANKS!!!

Sir, thank you so much. In such a nice way you explained everything.. I really appreciate your efforts.. Cheers..

Thank you for this explanation. I have listened to a few techs try to explain fuel trim to me, but this by far has made the most sense. Thanks again!

ScannerDanner, You are the man! you help the do it yourself community in diagnostics! no words to thank you enough

Go to my website listed in all of my videos or on my youtube channel page. I cannot post a link in here but search Auto Computers Troubleshooting d o t c o m (no spaces, all small letter). Fill out your name and email in the comments box and I will send you out some more info. about the ebook. Thanks!!

Thank you,l have watched a few vids on this fuel trim issue and couldn't grasp the concepts of lean means rich and rich means lean and how the computer manages the 14.7 to 1 ratio and reading a scan tool correctly.This was great!!!

Agree with your approach completely as far as waiting on the cat. code. Check the PCV hose under the intake for a crack. This is very common on the 2.0 engines, not sure about the 1.6. I have seen also on Fords the stem area of the EGR worn out. When I changed my EGR on my explorer I had a 10% improvement in my LTFT. They all leak a little in this area though. Even the new ones.

Yeah, I got the electronic edition of your book last week. It makes a big difference when you have the background and fundamentals.

Wow this is one of the best videos on how internal combustion engines work i have ever seen. This was extremely well explained and helpful, thank you.

You do such a great job explaining this. I own a 2008 Toyota Camry 4cyl With no problems until it developed the fabled oil consumption problem. It didn't throw any codes... just burned one quart oil per thousand miles. Well, to Toyota's credit they wrote me and told me to bring it in because they had identified that model was having that problem. I had gone to the dealer and they had pleaded ignorance. Long story short, they replaced all four of my cylinders. 5 miles after leaving the dealer's service facility the car through a PO171 code and acted like it was coughing up blood. I hurried back to the dealer's but they had closed. Had to drive the car over the weekend and it got better and better.... But the PO171 code stayed. Well the dealer at their own expense replaced the intake head gasket, checked the fuel pressure, said they found a crack in the PCV hose, added a can of 44K and finally put in a A/F sensor (at my expense) based on a P2238 code. None of these worked to stop the PO171 code. Additionally, soon after occasionally the car developed a condition in which it would not start after being driven about 20 miles and if I would stop it would not start. On these occasions I found if I waited 20 minutes or so the car would start. However, it would start if I sprayed some starter fluid in the intake. That was three visits to the dealer at their expense and they could not find the problem. Otherwise the car drives fine. So I'm left with trying to find a problem myself or as they said wait until it just want start. I have waited a year. I have looked at your and other videos, Google articles, etc. I have changed spark plugs, air filter and checked for air box leaks. The car is too good to be just junked even though it has 280,000 miles. After all it is a Toyota. I have had no problems with it until the oil problem. It has stumped the dealer and me. But, I am trying to diagnose some things. I bought a scanner. I am not mechanic. Bought a generic live data/1 parameter graphing scanner out of desperation because dealer could not find the problem. At idle....the scanner said; 2008 Toyota 4cyl 2.4 LXE @ 900 RPM right after start up 122 degrees F coolant temp STFT -3.1% LTFT +35 to 44% IAT 57 degrees MAF ???? CLoop except when snapped WOT the trottle when it temp went to OLoop After driving 10 miles: 670 RPM in idle CLoop 201 degrees F STFT +4.7 to +10.2% LTFT +34.4 to 44.5 % IAT 113 MAF .32 5.02 (very varyable) O2SB1S1 -0.01 ma Cat Te11 635 degrees F Cat Te12 341 F LAMBDA B1S1 1.000 BARO 30 (never varies a lick from this) At this point I cut it off. Again it would not start!!! Tried starter fluid still no start. Waited 20 or 30 minutes started up without the starter fluid. Acts just like an old car I had with a vapor lock problem.

Thank you so much. 10 years later and today I saw the light. I will now attempt to solve a reoccurring P0430 on my Toyodor. Feed the cat. I like it.

Man do I want to get my hands on verus scanner, God bless you. You do a good job training ur students, wished I had an instructor like you in my days lol 👍👍👍👍✌

Here we are 10 years later, to reference this well taught, valuable information. Thank you!

THAT WAS an EXCELLENT Theory of Operation followed by actual test of a vacuum leak, then an extra fuel injestion (not injection) and how the system can self correct. What you said about having LTFT positive 30% and STFT-30% can be confusing, but showing +30 and subtract (-)30 = "0". It becomes a little more simple at that point. Then it's up to the system to self correct, or delete the codes and wipe clean the fuel trim memory, then observe it with the engine running. WOW!

The most thorough video explanations upon this subject. Thank you very much bro!

I let your channel play on a large flat screen TV in my collision repair shop and so many people actually watch and pay attention to your videos and say I never realized how some of the computer stuff works in a car.

Thank you very much! Hope you are satisfied with it so far. Let me know.

That's what I leaned in school anyway. Awesome video. I've spent hours watching your videos. Truly the best automotive series on the net. Keep up the good work!

Flipping great info! At 55 years old, retired law inforcement, would love to be in your class!

This is prolly the longest video ive watch in youtube with no regrets. Love the contents you put up!!! Keep up the great work.

Thank you for your kind words. It means a lot. Paul

Mind blowing video. I have learned this before and paid a LOT in dollars to learn all this. I bought ur book very useful and ur videos are much useful. The difference between you and other is, you teach the theory and show how that theory can be used in real life, where as other i can see too much on thoery and very less or nothing on practical. You are great. Adding another point, even though i learned this theory from other, i always learn new things when you teach. Great.

Paul... Your knowledge of engine diagnostics has been very helpful to me. Earlier today I bought a scan tool that gives me more comprehensive diagnosis. And I've discovered about fuel trim issues which has determined of my engine running too lean. Just to give an example of the fuel trim readings. Long term is reading between 20 - 25%. And the short term is reading at 15 - 20%. Not to mention the idle is a bit rough. Anyway, I just want to give you thumbs up.

I just recently signed up for premium account. I'm diesel tech want to improve my diagnostic skills on Automotive. Thank God for wisdom scanner Dan has to share his knowledge with others.

no problem joe and thank you very much for the kind words

WOW... The amount of information in your videos are off the roof sir!! well done.

Thanks for taking the time to response, I live in NY so probably the fuel can in fact be an issue but in the past years we have try changing to better fuel grade and didn't see any good result. But I will give this another try since now I have a few devices to read live data from the car.Car has the IAT build into the MAF sensor according to the reading seems to be ok this past few days I get reading like 60 F as I start driving and engine get hot it get to about 96-114 F..continue....

I just want you to know that I learned a lot from your videos in the past 6 months. Swore off mechanics years ago, and haven't touched a car in 15 years. Bought a beater of a KIA sportage for $1000 that somebody basically beat up, and threw away. Leaves inside the valve cover. Failed smog twice. Bought unnecessary parts for it,and then found the secret hidden vacuum port, and plugged it. Bought an OBD ll scanner, and watched a gang of your educational videos, and have been able to diagnose, and monitor the vehicle. STFT modulates at both 0.8 and 1.6 on both sides, and the LTFT is at 2.3. Idles great, and performs really good. Thank you Scanner Danner. (Think I'll make a smoker just for fun).

I got me a BlueDriver just for basic stuff. And I'm starting with fuel trim graphs. Slowly gonna learn that module then buy a more expensive one. Thanks for your videos !! You guys are awesome !!

this is the best delivery of fuel trim explanation i have seen . big ups...

Great explanation and I will watch it at least one more time. thank you

Man...I've only watched half the video so far...I had to give my brain a rest for a minute! But by 26 minutes of your video I now understand why this stuff is a bit confusing. Why if you ask someone what the correct numbers for your o2 reading is they'll say "I don't know"...same for fuel trim. But I now know what long and short term fuel trims mean and it does make sense to me. I'm scared to watch the rest of the damn video! LOL Will my brain explode? LOL Great stuff man, thank you so much, the way you are explaining things is working very well. I've had instructors in college that made my brain HURT and I loved it! Others the class was over and I really didn't feel like I knew all that much more about the content. So, again, Thank you!

Finally! a entail comprehensive tutorial on the subject of fuel trim.. Thanks! Dan for bringing clarification to this subject..

Thankyou for putting this one back on, people don't know know what they are missing if they dont have your book and class, Mary Christmas

Another excellent training video. I found out the hard way that clearing the fuel trims after repair will come back to bite you. German cars are kinda like that. They will chew up your ASE patch and spit it back at you! It’s nice to drive the car and watch those trims return to normal.

Explained very well and I liked the real time demo. Thanks

Best demonstration explaining fuel trim I have seen. Great job! Thank you

Wow what an excellent video on Fuel Trim data. I'm trying to diagnose my own car issue, as the car has a very nasty smell on cold starts, and this is helping me a lot. Thank you ScannerDanner.

This is so good i didn't have this knowledge when i was studing in my country. I'm gona buy your book it will cost me over 200$ but i dont care it's worth it. You are doing great job and you are exelent teacher.

Great content, the best video I've seen so far on fuel trims. I'm trying to learn how to tune fuel maps using fuel trims. This was very helpful.

Excelente explicación, ahora si entendí completamente los ajustes de combustible, y eso que tengo que traducir el video para poder entenderte. Gracias.

Excellent informative lesson, I learned a huge amount.Thank you very much for taking the time to explain something that I struggled to understand before.

Skinny Dana this is Donny here I like your videos don’t have much money but I like what you do and I have trouble reading and writing

thanks for your very kind words.

A great thank you from Greece for the education we are given

This is a GREAT VIDEO. I reset my KAM and watched my car learn its LTFTs at idle with my scan tool. Sometimes the vac leaks though can be very difficult to find or expensive to fix. I just fixed a nasty one around a leaking IMRC end using a RTV and a nickel. I went from 20LTFT to 6. I know the other side is probably leaking but its not worth bothering!

I hope your students comprehend the benefit you are to them & take full advantage

You have wisdom beyond your years, SD.

Well done !! lean and rich apply to both the O2 as well as the amount of fuel confusing for some people. A lot of people think the O2 reads amount of fuel and not oxygen. I help out at an auto parts store and lots of customers buy O2 sensors because the scan tool says so and it's normal for them to come back and say the sensor we sold were defective because the light is still on. I try to explain O2 readings to customers as a rich oxygen level or a lean oxygen level.

Experience Gained, Thanks Forever Danner❤

That's great man, thank you. You will not be disappointed

I think they should have instuctors from all these schools do videos to see who you would most relate to the way they teach. why cant there be teachers like yhis in indiana. i would love to take a class with this guy. we need more techs like this guy. Thanks again for another great vid

I bought your book recently and this video made a few things very clear. Great stuff!

To answer your question,rich condition(excessive HC lack of O2) without the exhaust leak does not damage the cat,but put it to sleep.Therefore,your tailpipe CO and HC will increase and NOX will decrease.As soon as the rich condition is repaired ,the cat starts working again. What damages the cat is HC+O2 (lean misfire,low compression.etc) because it burns inside the cat and melts the substrates. But like Paul mentioned a rich code for OBD2 will set at %15. Thank you

This is awesome! I am verly trying to understand fuel trims. It is pertty awesome! I understand alot now. Spending my free time trying to figure out emission codes! I like check engine codes like this they make you think and they make you feel like you are the motor of the car trying to fix yourself.

Thank you for making your lectures available here. Please keep them coming! It's great to find college level training videos I can watch on my own time, and not have to pay a hefty tuition fee. Looking forward to purchasing your book(s). :)

hey this class was awsome all my year being a tech this is the first time i understand fuel trim thanks man

Ive been watching ur Videos for close to two years now .I am now convinced that You are an Automotive Genius!!!!!!! because of ur Knowledge and ability to effectively teach Various complex Automotive topics Very Unselfishly Simplifying this Info while using proper terms well articulating information maximizing the edification of all listeners Although I Know UR also doing I from the heart, I Hope You Make Millions you deserve it

Amazing teaching technic as well awesome knowledge! Greatings from Brazil!

That was a excellent video, finally understand how fuel trim works. Just bought your book, worth every cent.

Wow, this is a great video. I understand a lot more about the fuel trim and the relationship to the O2 sensor.

Thank you very much! Something to consider in the future thanks.

Nice, glad you liked it.

Excellent explanation. My short term and long term memory thank you!

Great video thanks to this i can now work out why my car is giving me a p0172 rich condition now i understand how to interpret fuel trims 👍👍

Thanks sir appreciate your efforts.I am from Kuwait and i always watch your videos .

man cant discribe how helpful this video is to me thanx alot i mean a lot one day i want to be like u ur a graet teacher well explained thaxs alot man

Recently stumbled across you channel... NEW subscriber and pretty much new to Diagnostic procedures. Your channel and EricTheCarGuy are my go to channels !!!!!

Great video, really has a great grasp of the engine controls.

Brilliant presentation .... many thanks for the upload ... fantastic insight into the overall strategy of the ECM and how the fuel trims report it's adjustments.

Now I understand !Thanks Paul for everything you do .Cheers

Good teaching Paul lucky that people who are in your class..

You the man! Appreciate you sharing your knowledge to the community💯🙌🏻

Thanks for the informative video, Just now I understand what's going on , I am gonna kick some asses in my school ....THANKS YOU ARE THE MAN Keep it up

Absolute TREASURE TROVE of information!! 😁👍👌

Rocked my brain. Deep thanks.

22 years wrenching. I can finally say I understand it.

I had to paus and laugh when you emphasized fuel flow. Really awesome stuff I absolutely needed.

This is fantastic. Such a wealth of information presented in a very digestible form. I echo all the thanks and praises on here. Have you ever considered putting together a video for the DIY tuner community? Say, for example, understanding how to tune under boost using something like an aftermarket Fuel/Ignition Piggyback Controller?

This video is being introduced to Korean mechanics. Thank you. SD.

Hats off for the knowledge you share thank you sir

and your simply genious when it comes to scan tools. show up eric the car guy sometime

thanks you soo much man !, I didn't get confused throughout the whole video whatsoever.. awesome job explaining :))

thank you paul great video... evry tme i watch this video i learn somthing music to my ears

@ScannerDanner thank you to the fullest💯

thank you!

thanks man everything you post is alot of help