MAF can die without die with no codes / softfail

[GoGators]

writing this in hopes it will help someone else along the way...

I was very skeptical that a MAF (mass air flow sensor) could fail and still be provide ODBII data that appeared appropriate throughout the RPM range. well, I am skeptical no more.

I was getting an occasional lean condition code, bank 1 and bank 2 (P0171, P0174). over the course of a few months i changed the upper and lower boots, all vacuum lines, fuel filter, disa valve, cleaned the MAF, smoked the intake, replaced the CCV and hoses with no success... when I check my fuel trim, my Long Term trims were steady at ~ 10-14 throughout the RPM range.

when I replaced the MAF and put ~40 miles on it, my fuel trims are holding steady at ~ 1, success!!

so yes, a MAF can definitely soft-fail and appear as though it is working just fine when you observe the live data feed readings on your OBDII scanner. mine was apparently ~10% off throughout the rpm range, very precise, but not accurate (for all you engineers)!!!!!

[GoGators]

sorry for abysmal subject... it must be to early...

[slater]

thanks for the good diagnostic info, regardless of typos. :)

peter

[az3579]

This is what happened to me. Eventually the lean codes stayed, though the car functioned fine.

[TigerTater]

Did you see a drop in mpg etc? Symptoms other than codes?

[JFern]

Interesting diagnostic info, and agrees with an article I just read the other day:

http://www.autoserviceprofessional.com/article/94982/Fuel-trim-How-it-works-and-how-to-make-it-work-for-you?Page=2

Basically, if you add your long term fuel trim number and short term fuel trim together, it should not be more than 10%. The article goes on to say that a faulty MAF will cause positive fuel trim numbers, as the sensor is under reporting the amount of airflow.

[derbo]

This is good to know. I will have to check my car. I've been hunting a lean code for awhile now.

[GoGators]

Other than the occasional SES light, not really any symptoms. Yeah, the fact that the LTFT + STFT stayed relatively high, throughout the RPM range is what finally convinced me to pony up and replace the MAF.. since the lean condition didn't get much better at higher RPM, it ruled out further vacuum leaks, which ofcourse is the most likely culprit.