What exactly is the mass air flow sensor?

I have been experiencing the occasional service engine soon light since about August. Car runs fine, but lately it came on more often, and stayed on longer. We are driving to Florida soon, so along with new spark plugs, and an oil change, I asked the guys who service my car to see why the light was coming on. He said the code indicated the mass air flow sensor. He cleaned it (for free!) and said that will probably solve the problem. I thanked him, and so far (since yesterday) it has not come back on. But, I really don't know what it does. Is it the sort of round tube just past the air filter (on a stock 96 Roady)? He said if it persists, a rebuilt one is about $175, which is I am assuming his list, which would be probably $80-90 if I bought it. If it is the part I think it is, it looks like it could bolt on in about 5 minutes. Any thoughts on all of this would be greatly appreciated. Thanks, Mark.

The MAF on our cars is a "hot wire MAF" - it's a thermistor - a resistor that changes its resistance as temperature changes.  The GM PCM runs current through it to heat the thermistors up, then the airflow over the thermistors cools them down.  If you know the intake air temperature, and since you already know how much heat you've put into the thermistors, you can then use the resistance to figure out how much air is blowing over the thermistors.  It's not quite as simple as this, but this is the idea.

Don't bother buying a new one.  I bet you more than half the folks around this forum have a spare they'd sell you cheap.  

BTW, never clean a MAF with anything other than spray MAF cleaner.  Don't use alcohol and Q-tips - they are super tiny and you don't want to break them.  Also, never clean it while it's plugged in and ESPECIALLY never do it while the engine is running.  

FWIW, I've had MAF codes due to corrosion on the wiring harness plug.  Check that before you replace a MAF.

It is the part you think it is, I have never had any problem with one. I know sometimes they need to be cleaned, as yours was. I would not worry about it and consider it fixed as you don't have any check engines light anymore.

Actually, I thought I had to replace mine last week, but I put my glasses to read the diagnostic printout and it was the MAP sensor that needed to be replace. You are correct about the price, somewhere around $90 is what I saw them selling for.

Tom

Don't buy new. They don't 'go bad' often because there are no moving parts. Get a used one from a junk yard (or here), spray with the MAF cleaner and install. 5 Minutes MAX time involved.

Just so I understand, the mafs is, as the name implies, a sensor? I see a small sensor looking device sticking out of the side of the round tube behind the air cleaner, heading toward the motor. Sherlock, you mention using a specific product to clean it, and not to do it while the car is running. You don't say this, but are you supposed to remove the sensor, clean it off the car, and then re install it? If so, it sounds quite easy. Since my earlier post, I've driven maybe 50 miles today, and the light is still off. Is cleaning the sensor something that may be thought of a routine maintenance? Thanks guys for your response.

Mark, go to your favorite big box/parts store and pick up a can of MAF cleaner. Use it every time you change out the air filter. You can use it while on the car, just spray it into the honeycomb screen to clean everything. You can also remove the MAF if you want, but it is not required.

The reason I say the MAF must be unplugged is because at least on some models the PCM will periodically heat up the MAF wires to burn off crud with the engine off, and if you spray it while they're hot, you will thermally shock those tinys and may break them.  It's the same reason why you never spray it with the engine running.    So just as a safety precaution, unplug the MAF and let it sit for a bit before you spray.  

Use this stuff:  (although the performance claims are baloney because the PCM will recalibrate itself within 10 minutes and stock WOT fueling is pig rich anyway)

I just use electrical contact cleaner. It's also safe to use.

jasonlachapelle wrote:

I just use electrical contact cleaner.  It's also safe to use.

But does it gain 4 to 10 HP as CRC does?

Tom

Thanks guys. This is why I love this site.