How do you check a MAF sensor?

[Popinski]

Shucks. I got a Check engine light because of the Mass Air Flow sensor. I took apart everything from the Air intake all the way to the Throttle body and cleaned everything.

-I cleaned the throttled body with carb cleaner
-Cleaned MAF sensor with CRC MAF sensor cleaner
-Clean air tubes with sensor cleaner.

After putting everything back together, everything went fine for 5 minutes. All of a sudden, my idling went erratic and my MAF sensor check engine light came back on.

Question: I have my ohm meter with me. How do I check the MAF sensor? What readings are considered normal? I saw a video on youtube and the guy said 11.8 milliohms for his saturn.

I really hope that I don't have to take out $200 to buy another MAF sensor!!!!

 

[GMBoy]

This may sound low-tech, but it's actually one procedure outlined during MAF diagnostics in GM service manuals - you tap the sensor with the handle end of a screwdriver or small hammer lightly. If the you get a stumble or other idle fluctuation - the sensor is bad.

That's only one check, the other check involves looking at the readings it is giving with a scan tool or meter and comparing to known values in the service manual. Each car may have different normal values, of course so the factory data is key.

 

[Popinski]

GMBoy, you're right. Thank you. I also found this just now:

1. If the engine stalls occasionally, start the engine and shake the MAF sensor harness. If the engine stalls, check for poor contact at the MAF sensor connector.
2. If the MAF sensor output voltage is other than 0 when the ignition switch is turned on (do not start the engine). Check for the faulty MAF sensor or ECM.
3. If the engine can be idle even if the MAF sensor output voltage is out of specification, check for the following conditions;
a. Disturbed air flow in the MAF sensor, disconnected air duct, and clogged air cleaner filter.
b. Poor combustion in the cylinder, faulty ignition plug, ignition coil, injector, and incorrect comparison.

4. Though no MAF sensor malfunction occurs, check the mounting direction of MAF sensor.
USING VOLTMETER
Check item Engine state Test specification
Mass air flow sensor output voltage (MAF sensor side connector No.1 or ECM harness side connector No.41 Idle (800 rpm) 0.7 - 1.1 V
3000 rpm 1.3 - 2.0 V

a. When the vehicle is new [within initial operation of about 500 km (300 miles)], the mass air flow sensor air quantity will be about 10% higher.
b. Use an accurate digital voltmeter.
c. Before checking, warm up the engine until the engine coolant temperature reaches 80 to 90°C (176 to 198°f)

 

[SteveSRT8]

I have had extremely high mileage GM products throw really big voltage numbers and then reduced them right down to at/near factory spec with MAF cleaner.

I am completely sold on the stuff. It can save the cost of replacement.

 

[mechtech2]

You should be throwing a code. Have it checked - it may be 'hidden'.