Dirty MAF Sensor Case Study

[@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!

[@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

[@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.

[@DavidSmith-mk7qo]

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

[@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!

[@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!

[@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..

[@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.

[@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!

[@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!

[@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]

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

[@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!

[@ScannerDanner]

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

[@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.

[@sebsbae9149]

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

[@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.

[@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.

[@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.

[@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.

[@FixItAngel]

awesome diagnosing!!

[@billrimmer5596]

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

[@MrMratni]

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

[@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.

[@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.

[@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

[@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!

[@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!

[@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]

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

[@ScannerDanner]

Thank you so much. I truly appreciate the support

[@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]

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

[@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.

[@ScannerDanner]

The car most likely also had some fuel trim trouble codes too. If the MAF is reporting the wrong airflow the a/f ratio will be completely wrong and this can cause misfiring. Usually this is accompanied by lean or rich trouble codes as well.

[@DDR233]

Does the sensor under report or over report when it’s dirty? I get that the O2 shows lean and it’s dumping fuel, but it’s only reading lean because of what the maf is reading. So does that mean the maf is over reporting airflow? If that’s the case why are airflow numbers greater with the clean sensor? I’m just confused as to how the MAF causes the O2 to misread if the calculated air was less with the dirty sensor? Am I misunderstanding and the maf is under reporting and it’s fueling for what the MAF thinks is passing but the actual air charge still passes and leans out the mixture the MAF thinks it is dealing with? Then that causes the pcm to infinitely rich the mixture because it will never record absolute air flow

[@ScannerDanner]

@@DDR233 a dirty MAF will under report airflow under loads. Some will over report at idle only, but both types will under report under loads. This causes the base fuel map to be skewed as the engine load is being under reported too. So positive fuel trim numbers result. Positive trim numbers does NOT mean rich!! It is a rich command caused by a lean condition.

[@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]

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.

[@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

[@ScannerDanner]

Yes A MAF DTC with good MAF sensor usually sets a “range/performance” code and may be caused by the following: TPS problem Vacuum or air intake leak Oil cap or dipstick problems PCV system leaks Dirty/plugged air cleaner clogged exhaust

[@ethereous]

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

[@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.

[@ScannerDanner]

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

[@ScannerDanner]

typically not but it is possible. you need to start by checking your fuel pressure and checking for a ruptured fuel pressure regulator diaphragm

[@ScannerDanner]

Low MAF grams per sec at WOT, also low voltage during a snap while we were testing it directly under the hood. These were the clues that the MAF was the problem and not fuel pressure.

[@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.

[@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

[@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)

[@ScannerDanner]

I don't think there was a problem at all with the scan data. I think this was simply a small engine that doesn't "breath" the same amount as other engines do. Remember every car is different as far as what peak grams per sec will read.

[@ScannerDanner]

The check engine light will set the other two lights. They are the traction and vehicle stability control systems. Fix the check engine light and you will automatically get rid of those other lights

[@cbobcbob100]

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

[@ScannerDanner]

if the o2 is switching before the wot run then it is not an 02 problem. it is a fuel delivery problem. low fuel Psi and dirty MAF are the top two. a severe misfire can also cause this

[@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.

[@ScannerDanner]

If it was a 2 bank system then yes, a dirty MAF would affect both banks. But this is only a 1 bank 4 cylinder engine. Bank 2 doesn't exist. Great question though, it means your thinking!

[@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

[@ScannerDanner]

No the hissing is tank vapor psi not fuel psi and will have nothing to do with your lean exhaust code. An EVAP code maybe but not a lean exhaust.

[@ScannerDanner]

@contagiousFX What numbers? Fuel trim should be +/- 10% MAF grams/sec and frequency will depend on year and engine size to name a few. For most of the GMs I look for at least 150 gram/ sec at WOT and a frequency of over 8500HZ, Idle would be around 2.3-2.4khz. But again there are variable.

[@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.

[@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.

[@ScannerDanner]

not a dumb question. you cannot use the downstream sensor the same way because the cat catches and stores oxygen. there is some diagnostic advantage though but it is not used the same way. check out my o2 fixed lean case study

[@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

[@ScannerDanner]

There are other causes of those lean exhaust codes. Sounds like you need to take it to a competent mechanic. It doesn't matter if he is an aftermarket guy or a dealer guy. Go to iATN and search for garages in your area. If they are iATN members you have a better shot at a good tech.

[@ScannerDanner]

@lesbirel91 A dirty MAF is not the only cause of a lean exhaust trouble code. If you have my book check out Section 5 page 5. The list on this page address the most common causes for P0171 and P0174 DTCs

[@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.

[@BRILLOPADral]

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

[@exit9mastertec7]

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

[@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]

Close. Low fuel pressure will also be an under load lean condition just like a dirty MAF

[@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!

[@scootfd3s]

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

[@ScannerDanner]

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

[@ScannerDanner]

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

[@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.

[@jamesbarratt593]

There really are some dumb ass people in this world. Just reading the excessively high negative comments on this video whereby they all miss the base point Paul's doing. He's educating us on scan tool info, the airflow O2 signal and the volts produced by the mass air sensor. He even showed the colour of the wire he was connected to. OK out in the real world he would have maybe just jumped to the mass air and cleaned it before test driving and realising the cars fixed, yet as with me who charges per hour; that wouldn't help. My earnings would plummet if I fixed the ride in minutes. I like this video and think those negative people should open their minds a little. Well done Paul. Cheers for that.

[@ScannerDanner]

Yea, I know I should take it off as I am not showing proper safety procedures with it on. I am super careful of where I put my hand and truthfully I would rather take the chance than take my ring off. It is sacred to me. (I do take it off if I am reaching my hand near a starter motor or alternator that I cannot see very well)

[@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]

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

[@PineHollowAutoDiagnostics]

haha I actually used a fine-tipped dental pick, but don't tell anyone! A little compressed air helped too. Those wires were pretty gunked up...not to mention his airbox was full of dry leaves lol

[@ScannerDanner]

I am not sure. I know some guys use this initial spike to determine if the MAF sensor is dirty. I am just not familiar enough with the procedure.

[@luismartinez4198]

I read somewhere, that when you have a fuel related lean code, as you rpms get higher, the fuel trims go high really fast; but for a MAF issue, the fuel trims have a slower increase.

[@abdul-kabiralegbe5660]

Thanks. I was trying to see how to differentiate between the two. This is why I like to read comments on a video.

[@ScannerDanner]

Higher than normal Co means the car is running rich. If you have my eBook, Section 5 page 4 gives a list of causes of richer than normal conditions. Here is the list:Higher than normal fuel psi Ruptured fuel psi reg. diaphragm Leaking fuel injector EVAP purge problems ECT or IAT sensor problems MAP/BARO or MAF sensor problems EGR valve stuck open at idle Fuel contaminated oil Head gasket leaking causing coolant contamination of the O2 Jumped timing chain/belt

[@tonylexmark]

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

[@ScannerDanner]

I believe it is a hot wire type but you should pull it out and inspect it first

[@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.

[@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

[@mechanic4yourcar]

The whole video is very good filled with good information.

[@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.

[@Autofixpals]

on vehicles (i believe all of them now) with electric throttle bodies. Will you be able to do WOT snap test? what i notice (chrysler is the worst offender) is that when i try to Rev it the ECM stops the fun. What should/would you do in that situation?

[@ScannerDanner]

+Auto Fix Pal if it is an automatic, with key on, engine off, put the transmission in gear. (block the wheels of course). This should allow the throttle to react to the app sensor

[@Autofixpals]

+ScannerDanner awesome. Thank you.

[@kenmh7357]

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

[@JoelAutomotiveInaction]

Paul do you know how this circuit works (maf sensor) I was working. On 2000 ford focus the maf sensor has 6 wires Pin 1 And 6 are for air sensor . The pin #2 has system voltage ( 12v). On the pin #5 is coming out the sensor signal to PCM at wot about 4 volts . But on pin 3and 4 I have ground . How that works . This was perform on not working maf I did. Not see any signal so I decide ti check power and ground and I did not find any 5 volt reference any way I replace the maf and it fix

[@ScannerDanner]

there is no time frame, it is a learned value and will constantly adjust if needed. Every run period there can be small changes with it. After a repair, it will correct back to normal values while driving the vehicle. Watch my video "Understanding ST and LT Fuel Trim"

[@ScannerDanner]

Thank you Joel!

[@carrotecnicatreinamentosau7217]

Excelente estudo de caso. Obrigado!!

[@mikezaldivar8562]

The VVT-I configuration did not exist on the 98 Corolla, it started on the 00 model year. Check your fuel pump pressure. Had the same problem on my 98 Corolla at around 200,000 miles. New fuel pump cured the problem.

[@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?

[@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

[@KaldekBoch]

Hey Dan, does the rule of the improvement in fuel trim at rpm also apply to boosted (turbo/super charged) motors? My suspicion is that the rule wouldn't carry over to a boosted engine because air leaks still cause problems under boost.

[@ScannerDanner]

+KaldekBoch yes, it still applies. But you will not be able to see peak MAF voltage in the shop. A test drive is needed. kzbin.info/www/bejne/h6iqenaBpryag5Y

[@ScannerDanner]

holy Crap. that could be the lowest baro reading I've ever seen on a ford. it should be running ultra lean with that number. you have any codes

[@ScannerDanner]

thank you

[@hp11208]

how would i test a maf with a multimeter, on a 01 maxima code po171.