Knowledge is power…. and about that mass air flow sensor.

*non technical post* Knowledge is power.... and about that  mass air flow sensor. 


I failed my car emissions test the other day.


I am a procrastinator and when my car tabs are due, I wait until they are just about to expire before I head down and get new ones. I know, I can even get them by mail nowadays – but that has not affected my behavior.


In WA, you need to get an emissions test every other year in order to get new tabs. This was my year and  the car failed. They never even bothered to check the exhaust from the car, simply plugged in the computer reader dealy thingy and read the code – bam – automatic failure. Code was P0171 – otherwise known as “System Too Lean - Bank No. 1.”


Now, Ill be the first to say that I know next to nothing about cars, but I know that I should have had it looked at before spending the money on an emissions test.


The check engine light had been on and off for at least 6 months. But, when I took it in 9 months ago ( just to see why the check engine light was on) they charged me $80 to turn the light off and said that nothing was wrong with the car. Ahh .. knowledge is power.


So this time around I decided to do some homework and found that it most likely is something called the “mass air flow sensor” or the “o2 sensor”. There are some nice folks on IRC who helped me out here.. ( thanks  bofh ) Great. Which one is it, heck if I know.  I  randomly chose the mass air flow sensor.

 Here is mine.



 Bummer – some casual looks on the internet suggested a mechanic would charge between 300-600$ to replace it. Looks like parts cost around $100. Here is a side thought – when I started my search I used words like “mass air flow” and “Nissan maxima" - as I moved on and read more I noticed many sites using the acronym “MAF” – so I extended my search to use  "MAF"  and "symptoms".  Again - knowledge is power… secret little acronyms us non-auto mechanic inclined are likely to know. J


Also - I wonder how we improve the search engine results by doing the same thing automatically?


Well – in the end I got lucky and found it was covered under my warranty w/ a $50 deductible. Great!  I call the dealer – yessir, its covered… yessir we can get you in today. Excellent.


Dropped the car off and they said they would call me with the diagnostic results. If it turned out to be something NOT covered by warranty I cover the cost of the diagnostics and the part etc.. else I just cover the 50 bucks.


So a few hours later I get a call.

Ring Ring.  



Well you were right sir, the mass air flow sensor needs to be replaced. It will be $650.


Umm no.  No I don’t want my belts changed, nor my fluids flushed nor my injectors cleaned nor etc… etc.. All I want is the MAF sensor changed.

OK – we understand – one MAF coming up.  $50.   But sir – we also need to upgrade the ECU and that will be another $110.



The what? Gahh.. I scramble on to the internet - ECU...ECU...ECU -- WTH  is an ECU? AHaha!  Wikipedia saves my pride --


While the mechanic is on hold I read as fast as I can – why do I need the computer in my car flashed when I replace the MAF? Unknown to me.  So, I get back on the phone and ask him.


Well sir, there have been some upgrade to your ECU and it needs to be calibrated for the new mass air flow sensor..


                (silence) * I am thinking about it, but he senses my hesitation and scrambles to save the sale*


OK Sir, I know you cant tell what the ECU does and it seems like you aren’t paying for something tangible, but I assure you that you are. Tell you what - ’ll split the cost with you and cut it in half - $50 for the ECU upgrade.


                Ummm.. OK I guess so.  Go ahead and bill me 



After the phone conversation I had a chance to think about it and smelled bull****  So I run upstairs to a guy who knows cars. “Hey Gale ….” And proceed to tell the tale.  "Do I really need an ECU upgrade?" Nope.




I called a different mechanic in the city - Gregs  Japanese Auto   - answer  - “Nope.”


Knowledge is power.  Later that day I discuss it with a colleague – he likens it to someone who can barely use email and just got a computer. When something goes wrong - how do they know they aren’t getting snowed? They don’t…  Someone could come and tell them they need a new HD, new fans, new video card – whatever – and they would blindly nod “umm ok please let me know when its done”


Knowledge is power.  I just don't have the time to gain all the knowledge ( power ) I need to when it comes to cars.




Comments (6)

  1. mikeshep says:

    Maybe you could swap out the MAF yourself, hold it in there with scotch tape and I bet someone like Colby could engineer a cable for you to plug into the ECU on the car and your USB port to flash the ECU yourself…

    Better yet, see if you can use Gale’s lift, then abandon  your car on it with the new part on the driver’s seat.  He’ll probably replace the MAF for you just so he can get it out of the garage…

  2. SpatDSG says:

    All great ideas .. why didn’t I think of the scotch tape???  Oh wait.. I did.

    As far as flashing and colby… I dunno about that. With my luck, I’d end up with a large hunk of metal.


  3. mike says:

    becareful when hooking things up to your ECU. Nissan ECUs are programmed to fry themselves when tampered with.  You can disconnect the negative battery terminal, on most nissans, to clear the ECU. Try a disconnection for a half hour.  When the battery is reconnected, the ECU will relearn every sensor’s condition.  

    I failed emissions too. (NJ)

    I have tried two used MAFs. My 93 maxima just wont pass.  I am going for a aftermarket remanufactured MAF sensor. It is remanufactured from a nissan core. As a former Nissan technician, I strongly discourage aftermarket electronic parts and sensors.  Example: many times, a nissan would come in for a "no start" or "poor running" problem. In many cases, I would remove the new distributor cap (made in Italy) with an old nissan cap, with 20k miles on it.  The old nissan cap would fix the problem.  Nissans can be very particular with electric parts and sensors. Yet, $125 for a remanufactured aftermarket MAF, made from an original Nissan core, is so much more tempting than a new $400 MAF from the dealer.

  4. Daniel says:

    Question since apparently several people in here seem to know a bit about MAF sensor on Nissans.  I have a 2001 Nissan Sentra and the **** who owned it b4 me removed half of the air filter box and the previous air filter (K&N) needed to be replaced…done.  I am in the process of acquiring the missing half of the air filter box but in the mean time, the car idles really rough and if I give it too much gas, it almost stalls and dies.  You can hear it trying to "breathe".  The hose that connects to the MAF sensor broke off and I was able to reattach it until I can get it replaced but I get the feeling the MAF sensor may be bad and tomorrow is my only shot to replace it if possible.  Can this be done myself and do I need to get the ECU professionally done or just disconnect the battery and reconnect it later to let it "pick up" the sensor settings?  Thanks in advance for the help.


  5. Way off topic.. Well lot’s of things been going on lately. First off I learned how to fly fish! Man it

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