Does a MAF receive inputs, or just send them?

Hello, 

I know a Mass Airflow Sensor sends a signal to the pcm which influences the adjustments the pcm makes.  But does the MAF 'receive' signals from other components to make its grams per second signal?  I assume the MAF only reads the incoming air coming through the intake snorkel and simply displays the grams per second as the hot wire is cooled by the amount of incoming air.  Long story short,  I'm wondering if a MAF seems to be displaying the wrong grams per second,  could another component be to blame that's influencing that MAF reading,  or would I just have to blame the MAF itself since it does not receive any inputs from other components?  Specifically the car I am referring to is a 2007 Toyota Camry 2.4L

Timothy,

Generally the air intake temperature is an important factor for correct mass air values.

A wrong or missing MAF sensor reading may be concealed by what's called 'substituted value'. An obviously irrational measurement is ignored and the control unit will display an inferred, calculated value based on other inputs. A substituted MAF reading could be made based on map, baro, iat, rpm data for example.

You will find substituted values only on the OE side of a scan tool.Not all manufacturers use them. They are not a allowed within OBD2, the sensor data shown there MUST be truly measured value.

Thanks!  I checked in both OEM & generic scan tool mode and found the MAF g/s reading as low as 1.9 g/s on my wife's 2.4L Camry.  I've checked that PID in the past when the car was running fine, and at idle, AC off, it normally reads 2.4 g/s, matching the liters of displacement of the engine.  The g/s at idle, no load, can show a little higher than 2.4 g/s at times, but I've never seen it swing that low.  

She noticed some drivability symptoms and the check engine light came on with a P0101 MAF code, as well as a system too rich code.  All powers and grounds look good to the MAF but I've never seen scan data show grams per second that low on her 2.4L engine.  I'm leaning towards thinking the MAF is mis-reporting the incoming air.

I verified the IAT signal and temp looks good, the MAF sensor wires look perfectly clean, the air filter looks good, and no damage to the intake snorkel.  Does a MAF in generic mode, showing much less grams per second than liters of displacement at idle, no loads, sound like a mis-reporting MAF signal, or could external factors cause the MAF to show low g/s?  

Thanks so much.

`Any air leak on the intake side will affect the reading be it a manifold gasket,an injector O-ring.....

The 1 gr/sec rule is not written in stone, especially on smaller engines (under 3L).Other design features like miller cycle, VVT may influence as well.

How does the fuel trim behave under varying conditions: idle, 1500 rpm 2500 rpm?

Thanks!  I did check the fuel trims under those two loads a few days ago.  If my aging memory isn't failing, seems I remember they were around 5ish total at 1500 rpm and around 9ish around 2500.  

timothy.spencer wrote: Does a MAF in generic mode, showing much less grams per second than liters of displacement at idle, no loads, sound like a mis-reporting MAF signal, or could external factors cause the MAF to show low g/s?  

In addition to what Juergen has suggested, there's also the possibility of airflow issues upstream of the MAF that can cause the MAF to misreport. Missing air filters, aftermarket air intake tubes, like that. The OE design usually incorporates features that create laminar airflow going into the MAF so that it gets a good sample. When those features get screwed with, that laminar smoothness goes out the window.

It's not a very common condition, but it can happen. GM released an interesting TSB for a similar issue on their '16-18 Cruze:

static.nhtsa.gov/odi/tsbs/2018/MC-10137584-9999.pdf

Not saying that's the case with your Camry, just a possible external factor.

Thanks for this reply! Sorry, I just now logged back in and saw it. I'll check this out.