Dirty MAF Sensor Case Study

2000 Toyota Corolla MAF sensor testing. Using a scanner and labscope.
Trouble code P0171 in memory. How to determine what is causing the engine to run lean.
Symptoms:
- low power
- hesitation
- check engine light with a P0171 fault code
Fix:
- clean dirty MAF sensor
Test procedures shown:
- how to test a mass airflow sensor
- how to use a the oxygen sensor at wide open throttle to test fuel delivery
- before and after cleaning scan data and scope measurements of the MAF sensor
- throttle position sensor will not reach 100% on scan data
- how to clean a MAF sensor
Tools used:
- Lab scope
- Scan tool
- Back-probing pins
- Brake cleaner/MAF cleaner
Related videos:
- How to troubleshoot a faulty MAF sensor
• How to troubleshoot a ...
- How to test a Ford MAF sensor
• How to test a Ford MAF...
- How to identify and clean a dirty MAF sensor
• How to identify and cl...
- How to identify and clean a Dirty MAF Sensor
• How to identify and cl...
- False MAF sensor trouble codes (cracked air intake tube)
• Low power, lean condit...
- MAF and lean codes from a missing air filter (P0171, P0174, P0102) • Cold Air Intake Warnin...
- How to test a 3-wire MAF sensor (wiring and sensor tests)
• Substituted values (Sc...
Playlist:
- (Chapter 12) Mass Airflow Sensor Testing
• (Chapter 12) Mass Airf...
For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium www.scannerdanner.com/join-sc... There is a 14 day free trial.
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!
Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, 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 ScannerDanner LLC.

[@PineHollowAutoDiagnostics]

Working on my friend's 2000 Tacoma truck today. Same P0171 code, plus a P1133 (A/F sensor circuit response). Drove around, long term FT topping out at +39% at higher engine loads, but negative at idle. This video instantly came to mind. Checked fuel pressure just to make sure, then went after the MAF. BINGO! A little electronics cleaner and a light brush...truck drives like new now! So why don't these sensors have a self-cleaning burn-off circuit like older MAFs? Once again,you're the man, Paul!

[@Airman..]

you never over killed a single video on your channel cause your knowledge is priceless

[@ScannerDanner]

thanks so much!

[@ScannerDanner]

Yes. The MAF sensor is actually a mini computer. All of the conversions are done inside of it. All computers need a main power and ground to work. So you can think of the 12v feed and ground on this MAF sensor as the same thing. IT is actually a MAF module.

[@FixItAngel]

friend had a '01 Lexus GS300, P0171 and P0174. Did exactly what you showed on your video with my ETHOS Snap On and figured it out. Thank You!! Though I worked at a dealership for 7 years as a used car tech and graduated UTI, nothing compares to your skill. I hope I can get to your level. Next buy is your book. Thanks again.

[@lyleandres1510]

A trick: you can watch series at flixzone. Been using them for watching a lot of movies recently.

[@karsonali241]

@Lyle Andres Yea, I have been using flixzone} for since december myself :D

[@DavidSmith-mk7qo]

I have seen a bad MAP or MAF cause poor mileage,transmission issues, and even a no start. Good video.

[@FixItAngel]

awesome diagnosing!!

[@JohnMcClane99]

Thanks alot! My hilux has been missing and hesitating for weeks, I had done some AFM testing and given it the all clear. Your video made me go back over it and sure enough, it was filthy. Quick clean and it's back to normal. I was just a couple of days to taking it to a workshop and probably copping a $500 bill! Love your work!

[@TheJaxonj]

Thank You Very Much. I just purchased a 2000 Corolla and after changing the spark plugs didn't fix the problem I guessed it was the oxygen sensor. So $85 dollars later I was feeling a little worried when I still had the same problem and not sure where to go. Your video saved me a lot of time, worry, and most likely money. Just removing that little bit of dirt made all the difference. Thanks for the video!

[@ScannerDanner]

thanks man! keep at it bro you are at that threshold now where great things happen. experience is so critical isn't it? i have so much to learn still too. it never stops

[@mdanny445]

Awesome video, thank you for uploading! Always good to see the entire process explained properly, instead of just jumping to the fix. Very pro.

[@kevinemesiobi6169]

Great diagnostic strategy, Using just the scanner to narrow down on the fault, that's a show of in dept knowledge on auto-diagnostic.. Thumps Up......

[@ScannerDanner]

Thank you Kevin!

[@429psi]

This info is absolute gold! Best diagnostic videos on the web hands down. I highely recommend the ebook people, I will be buying the lecture videos also. Thanks for the wealth of info paul, keep up the good work!

[@mike-yp1uk]

this video is not for amatur mechanics. It is accurate and packed with infomation for trained professionals who may have missed or are trying to deepen there knowledge. You have to watch it a few times to gather all the info and check out other videos and spend some time studying. Great and accurate video as usual. thanks paul.

[@ScannerDanner]

Thanks mike r!

[@EP91STARLET]

Had an exact same problem on a 2001 Yaris and this gave me confidence to confirm my repair after I had cleaned the MAF, great videos!

[@ScannerDanner]

@mechanic4yourcar Thank you! With your creditials that means alot. I am glad you liked it. Thanks for watching.

[@chief455]

just bought a 2001 Corolla with code PO171 thinking O2 sensor, reading some tech found more likely a dirty MAF - this video is awesome! I not only see the how and why it makes sense - but your explaination helped me understand data I have been logging on a racing V8 car as well with fuel problems. this is internet at it's best, thanks for sharing!

[@ScannerDanner]

@beefystik Keep watching, more videos coming soon. Its crunch time for getting my book done right now so I haven't uploaded any new videos lately but I have 4 or 5 new ones already recorded. I just need to find the time to edit and upload.

[@billrimmer5596]

These videos r really valuable information. This was six years ago! Thank u Paul Danner!!

[@felplayvina]

After clean the maf sensor the idle is fix and running good for a test drive but for second test the p0300 came back but is not misfire a lot LTFT --10 on both bank.. thank you for the time I know your are working hard every day. god bless you..

[@ScannerDanner]

@lucky51762 Sorry, it was a snap-on verus and not all MAFs can be cleaned. Just the hot-wire type. Thanks for your comment.

[@ScannerDanner]

Thank you so much. I truly appreciate the support

[@MrMratni]

This is the best MAF diagnostic video. All your videos are very informative, thank you so much sir for uploading..

[@sebsbae9149]

El Paso TX right here... Keep it up ScannerDanner... this channel is music to my ears...

[@ScannerDanner]

@jdrums5555 Thanks for your comment. I am glad you liked it. For more resources check out my website, its listed on my channel page.

[@rickchapman3707]

I've been watching your videos for years and have been a technician for 30 years.. When i started to be really interested in MAF sensors i was seeing a hell of a lot of hot film style here in Europe.

[@cbobcbob100]

great info as always...love the ending with long and short term relearning....bob

[@higgout]

This is so awesome man. My 98 camry was running lean base on my fairly new plugs having ash like build up and power reduction at increased RPM. found you video and it surely help me to understand a bit more of whats going on. dont have all your test equipment but now know the expected output voltage from the sensor when I do my volt meter test. As an electrician I know the benefits of the right test equipment. great job on the video.

[@jdrums5555]

great videos scannerdanner lots of good info,i just graduated from ATS school in sacramento and i am getting ready to test soi am reading all my books and watching all your videos very helpful thankyou.

[@ScannerDanner]

@MrMratni Thank you very much and no problem. I am glad you liked it.

[@carrotecnicatreinamentosau7217]

Excelente estudo de caso. Obrigado!!

[@ScannerDanner]

@chief455 Thats great! Thanks for your response. It helps to know that this video was clear and useful. It keeps me motivated to keep filming more.

[@BRILLOPADral]

Really good tutorials, keep up the good work, we need more like these.

[@ethereous]

Absolutely fabulous video. I can't imagine this video being done better. Great info and great presentation.

[@PaulC1980]

Just subscribed to Your account,Your uploads are excellant,have learned so much in a short space of time.I will definitely buy your E Book,I've never had anyone to learn much from about diagnostics so i'm very impressed with Your information and delivery which is easy to understand.keep up the Good work from Paul in Ireland

[@blitzzfyre]

Cheers man. Just recently bought a Celica GT-S and suspect I'm having almost the exact same issue. Replaced Spark Plugs and put injector cleaner in, didn't help much with my lag. Figured it was a MAF Sensor issue. Going to clean it this afternoon and get back to you :) This vid helped a lot, cheers!

[@JoelAutomotiveInaction]

thank you , it was perfect answer, it clarified every question was in my mind. you know Paul I talked to my snap on dealer I made a letter for snap on he said he was going to handle to some one in chart there for diagnostic I told the guy you are teaching us how to use the verus and how to test the sensor with the tool on real vehicles problems I told the dealer guy you should get some credit for that I hope they do some thing you really deserve it.

[@richardashcroft4596]

Thank you Paul for this, my ‘11 Cruze LS has P0171 code. Will be testing this method on my way to work tonight.

[@ScannerDanner]

Thank you Joel!

[@ScannerDanner]

@RUSS16V2 Thank you very much and I will!

[@pablohernandez3271]

Thanks man! i just bought your book, this is my first video from it, thanks man!!

[@ScannerDanner]

Hope you enjoy it! Thank you so much!

[@ScannerDanner]

Good question, as for the vacuum leak issue. I have never seen that effect the baro calculation. Also after cleaning the MAF, you have to reset the KAM or disconnect the battery for awhile to clear the baro calculation in memory.

[@ericverster4069]

Great and thorough video

[@mechanic4yourcar]

The whole video is very good filled with good information.

[@kenmh7357]

This very informative. Thanks! Have a VW and waiting to get my OBD II Pro to get real data

[@SEXYTECH1000]

BRO, THE MORE I WATCH THIS VIDEO THE MORE I LOVE IT,

[@tonylexmark]

Superb video and very informative. To get rid of glare on your screen get a polarizing filter for your camera, cheers.

[@ScannerDanner]

thank you

[@mshmbo]

Thanks for sharing, very nice and informative.

[@georgedawsonjr450]

Thanks to Paul danner I can't look at vehicals the same anymore. The book he put out is worth every $ your pay. My life has realy changed thank you paul. I can't wait to see more videos and I'm really hoping you put out an other book I know there is more you have discovered to teach us. I soon will have my L1 certificate. Thanks to you again. Keep up all your doing its great.

[@ScannerDanner]

All new stuff right now is in the form of video lessons on my Premium channel. I may write another book someday, but for now, come join my classes! Thanks

[@jwilli2112]

Great video, very well done. Thanks

[@ScannerDanner]

Rosedale Tech in Pittsburgh Pa is the school and you can get more info. about my eBook on my website listed on my youtube channel page or search "Auto Computers Troubleshooting" on the web. Thanks!

[@scootfd3s]

Wow i cleaned the wrong part the whole time. I'm going to try again. thank you very much.

[@freddysoto6584]

Nice video. Always learning from you..

[@ScannerDanner]

+Freddy Soto thanks so much

[@oscarrojas4281]

You are awesome I just brought your book and send me here you're the man I'm learning a lot thank you so much

[@ScannerDanner]

Awesome! Thank you so much!

[@ScannerDanner]

@GamingJediPwns you are mistaken on that comment. this style of hot wire maf is not damaged by the cleaner i used. its just a heated resistor with a glass covering. I've been cleaning them this way for 15 years with ZERO comebacks

[@ScannerDanner]

thanks tony!

[@ScannerDanner]

nice thanks bro

[@ScannerDanner]

@Gizmopflege Thank you!

[@cagonesss]

yes i did the resistance check and found one injector at 5 oms and 3 others at around 9 ohms so i did have shorted injector ,was my starting issue.hey thanks alot for your help i was going crazy with this hard to find issue for 3 weeks .thanks again for sharing knowledge i saved alot of money doing it myself. gm 2.8 fixed good day

[@exit9mastertec7]

God dam ...this guy needs all the newer tools....scanner your the man

[@GRUSSNewton]

Great video! Keep up the good work!

[@onepaa1636]

Great test i like the veruss min max capability however i always use my dvom when reading o2 signals ive just been burnt to much with false readings but overall that was a great test got straight to the root without even having to check fuel pressure

[@ScannerDanner]

Sweet man, nice job!

[@ScannerDanner]

@MJRPerformance Thank you!

[@IamReadyToRock]

easy my friend. thnks from Peru

[@ScannerDanner]

Thanks! I was having trouble getting a clear shot with this design. Sorry about that

[@cbobcbob100]

great job-----thanks

[@ScannerDanner]

The IAT is a thermistor and the "cold wire" is possibly a thermistor, but the "hot-wire" is a resistor. (technically a thermistor is a resistor) Thermistors are generally used in voltage sensing circuits. MAF circuits measure the current flow needed to maintain hot-wire (heated resistor) temperature above ambient, then convert this to an electrical signal (analog or digital) that is proportional to the current flow and therefor in-coming airflow

[@jesusmalagon4336]

thanks Paul Danner very great video is very importan watch fuel trims and o2sensor thanks for all your time for shering us you are very great teacher thanks paul danner

[@bigold81electra]

Paul, MAF air flow depends on HP. The 2000 Toyota has 125 HP so max air flow will be about 110 gm/sec. An E39 M5 has 400 HP so max air flow is 350 gm/sec.

[@user-yt1cx7dv2c]

nice job.

[@jeremyshanks6937]

Another great video!

[@camryle5590]

Very helpful. Thanks man

[@ScannerDanner]

I'm ok with the initial drop lean on a rapid snap to WOT(sometimes you see that, sometimes you don't). Just make sure it stays rich the entire time after that.

[@kickblake]

If you're reading the values from a diablosport predator, I believe the output for the "baro hz" isn't the actual hz, its that number converted to "Hg based on a table. So a reading of 30Hz is actually 30"Hg...or approximately sea level.

[@ScannerDanner]

Yes as a matter of fact. Does this have a vane type airflow meter?

[@ScannerDanner]

@JohnMcClane99 Awesome! I'm glad it worked out for you. Extra money in our pockets this time of year is a good thing.

[@ScannerDanner]

@import0408 I hesitate to say all but most yes. The older vane airflow meters on some of the cars had high voltage at idle and it would drop under load, so opposite of the others in operating range.

[@W.Khairi]

A few observation here - The PCM didn't throw a MAF performance code e.i P0101 - u didn't look at the load PID or abs-load pid at WOT - I think at WOT injector ms is not calculated using MAF it is calculate based on built in maps, that at least has been my experience, Thanks a lot for information full video as usual.

[@xTAZER56x]

Great video!!

[@SEXYTECH1000]

THANK YOU SO MUCH, YES I SAW THE VIDEO , GREAT VIDEO MY MAN!!!!!

[@ScannerDanner]

Did you do the resistance check I showed in part 2 of the one video? This is your only option without a scope, unless you get lucky and the shorted injector is one of the two injectors you can get to without removing the intake. There are other causes of this condition on your car, but lets do a resistance check on the injectors first.

[@halleffect1]

haha, Paul's voice sounds like it's straining sometimes, but that's just b/c he's passionate about his work and wants you to hear over the shop noise.

[@ScannerDanner]

I've seen them set for only one bank but if you look at the trim numbers both banks are affected. It just flags one side because it is worse than the other. (sometimes)

[@felplayvina]

Hi Paul question about 99 frontier 3.3L code p0300 high idle about 1800 maf signal snap throttle 3.8V the maf has oil and the air filter too is this maf sensor can set P0300?

[@eduardokerr6322]

well explain thanks a lot i solve my problem

[@sulaimana.abdullah5989]

hi Paul. I love. your instructional videos. they are really very informative. what I need to know now is if my MAF sensor in a Lexus GS 430 could get damaged and how much they cost. cheers

[@ScannerDanner]

Of course you can damage the sensor if you're not careful. Thanks!

[@MM0SDK]

new subscribe from me mate. I'm loving OBD2 for the first time. I just wish we had all this when i was buzzing with car love 17 -22 yrs. I'm only 35 now but this was really new 15 - 20yrs ago. I would have loved all this back then. We just had rid of points back then....lol. ECUs were really only on the forced induction. Renault 5 GT Turbo....lol.

[@Pissed0ffKrzysztof]

Great Video, I can barely see 1 Thermistor (Temperature Thermal Resistor) when it was dirty at 07:30, and you can clearly see both afterword's at 08:56, Everything looks Clean, Dry, and Tight.

[@ScannerDanner]

i believe that is an analog type maf sensor and the signal should read more than 4 volts at wot redline. with a dmm you will need to drive it to see that number as the meter isn't fast enough for a wot snap test in park. You could also look at the stft and see if it tracks positive with a rise in the maf signal, this would also indicate a maf problem.

[@LynxStarAuto]

I've had this issue before and although I fixed it with a clean, the sensor eventually failed down the line. I just prefer to replace the sensors now.

[@ScannerDanner]

There are two grounds because the PCM MAF signal circuit actually gets its ground through the MAF sensor. So one ground is PCM to MAF and the second ground is MAF to the block. If the MAF to the block ground is bad, BOTH grounds will be bad. No 5 v ref. on this design.

[@ScannerDanner]

@03mazpro a dirty mass air flow sensor will not cause a catalytic converter trouble code. if all you have is a converter code and no exhaust leaks then you need to replace it. as for cleaning the mass air flow sensor as long as it is the style in this video then it is cleanable and brake or carb cleaner is fine

[@mdanny445]

Browsing through ur other vids. Going to enjoy watching them, SUSCRIBED! :-)

[@fermate1991]

I love your videos my friend...

[@ScannerDanner]

don't worry about the STFT with the engine cold and in open loop. The numbers are irrelevant. So do you have positive or negative fuel trim numbers when warm. mainly the LTFT is what I need

[@ChicoDeon]

YOU ARE THE MAN

[@mike-yp1uk]

that build up is call insulation and insulation traps heat. air coming in is designed to cool sensor but good insulation wont allow that. great case study.

[@rbarr1200]

This is great stuff.

[@JoelAutomotiveInaction]

Thank you for your response , so it receive 12 volts external the maf and some way inside the maf it is converted to 5 volts Out put sensir signalto PCM is that rigth?? Because on snap throttle I saw about 4 volts. Thank you , you are a great teacher