MAF TEST 3: Testing The 2nd Ground Circuit
Now, we'll check the second ground circuit of the MAF sensor. This ground is provided by the ECM internally.
CAUTION: When testing this circuit, you've got to be careful and take extreme care not to short-circuit this wire to power or you'll fry the Fuel Injection Computer.
OK, this is are the steps:
Put the multimeter in VOLTS DC mode.
With the black multimeter test lead and an appropriate tool, probe the wire identified with the letter letter C in the photo.
With the red multimeter test lead probe the battery positive terminal.
You should see 12 Volts on the multimeter. Do you have 12 volts?
Let's take a look at what your test results mean:
CASE 1: Your multimeter registered 12 Volts: This is the correct result, the next step is to make sure the MAF sensor has ground, for this, go to: MAF TEST 4: Testing The MAF Signal.
CASE 2: Your multimeter DID NOT register 12 Volts: Recheck all of your multimeter connections and retest. If you still do not see these 12 Volts, then this exonerates the MAF sensor as bad since without this ground it's not gonna' work.
MAF TEST 4: Testing The MAF Signal
Now that you've gotten the power and ground signals out of the way... now you'll test the MAF sensor's signal.
It's important that the engine be at its normal operating temperature. So, start the engine and let it reach it's normal operating temperature.
I know I'm stating the obvious, but the MAF sensor must be connected to its connector to perform this test. OK, let's start:
With the Key in the Off position, and your multimeter still in Volts DC mode.
With a suitable tool connected to the RED multimeter lead, probe the wire labeled with the letter D in the photo. Connect the BLACK lead to the battery (-) negative terminal.
Crank up the engine and get her to idle.
Once the idle stabilizes, take a look at the voltage number or numbers your multimeter is throwing at you. This voltage may fluctuate a little or a lot, and this is OK. Whatever they're doing, this is your base MAF signal voltage.
Now, open the throttle (manually) to rev up the engine. As the engine revs up... keep your eyes on the multimeter's voltage numbers. The voltage should increase.
When you let go off of the throttle and the idle comes back down, the voltage reading should also come down and should hover around the numbers you noticed at the beginning of this test.
Rev up and let the engine come back down several times. Each time, the voltage numbers on your multimeter should rise and fall smoothly.
If the MAF sensor is good, the voltage numbers on the multimeter should rise and fall smoothly and without gaps. If the MAF sensor is BAD, you see one of three things: 1.) you WON'T see a voltage registered on the multimeter at all or 2.) the voltage will stay stuck in one number or 3.) the voltage numbers will spike up and down crazily even when you're not accelerating the engine.
Did the signal rise smoothly with each increase in engine acceleration and stay steady at idle?.Let's take a look at what your test results mean:
CASE 1: The voltage numbers rose and fell smoothly and without gaps: This tells you that the MAF sensor is good and not the cause of the MAF issue or Diagnostic Trouble Code.
CASE 2: The multimeter registered 0 Volts or a voltage that was erratic: Recheck all of your multimeter connections and retest. If you still do not see the indicated voltage rising and falling smoothly, then the mass air flow (MAF) sensor is BAD. Replace the MAF sensor.
If this info really saved the day, buy me a beer!