# Why MAF sensor reads zero?



## monind (Oct 18, 2010)

My 96 Pathfinder is lacking some power when accelerating. In order to investigate this I hooked up OBDII scanner and looked at the life data. What I noticed was that MAF (mass air flow) was reading zero both at idle and under load. I backprobed the voltage at the MAF sensor connector. The voltage was increasing with RPM. So it seems the sensor itself is working fine. Does anyone know why MAF reads zero? There are no any DTC trouble codes which makes me wonder. I would appreciate any input. Thanks.

By the way, when I hook up this same scanner to my 00 Toyota the scanner shows MAF=10.115 lb/min. So it's not that the scanner is faulty.

Dmitry


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## jdg (Aug 27, 2009)

Could be that your ECU doesn't use the MAF input for it's calculations.
If you're able to read the "PID word", which is mode $01, PID $00, the 16th bit of the word should be set. The "PID word" should be a 32 bit value, 8 hex digits. If you know that, then you'll know if your ECU uses the MAF.
Seems a bit weird that your engine would NOT use the MAF, especially if it's installed and the voltage changes. Everything I've ever played with that has a MAF uses it. If I disconnect the MAF in my Nissan's (97 and 98), I get a code almost right away.
Could also be that the scanner doesn't like the Nissan for some reason. Both Nissan and Toyota vehicles in the late 90's/early 2000's used the ISO9141 protocol. Maybe try the scanner on another Nissan and see what happens?


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## smj999smj (Jan 1, 2006)

I've never seen a MAF installed on a vehicle in which it was not used by the ECM as an input device...and I can tell you that it is certainly used by the ECM for input on a 96 Pathy and any other Nissan you mind one on! My guess would be some sort of communication issue between the scanner and the ECM of the Nissan.


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## jdg (Aug 27, 2009)

I agree, and I haven't seen it either. I know a few of those Mustangs and Camaro's years back had firmware updates awhile back to either ignore the MAF's completely or disregard certain MAF readings or something along those lines.
On the Toyota, I wonder if that isn't a "calculated MAF" reading. I put my scanner on a friend's RAV4 a couple of months ago and got a MAF reading from the ECU. Problem was..there was no MAF anywhere in the intake stream! And a quick search for a replacement MAF for that vehicle came up empty!


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