TEST 3: Testing The VAF Signal With A Multimeter
Now that the basics have been checked, we'll check the VAF signal coming out of the sensor and going to the ECM.
There are two methods to test the vane air flow sensor on your 1988-1992 2.2L Mazda 626.
The method in this test section is the one that I recommend since it's the most accurate way of testing the VAF meter.
The other method is to test the sensor dynamically (with the engine running) and you can find that test in TEST 4.
In this test section we're gonna' manually actuate the VAF sensor's measuring plate (vane) while we test the continuity of two specific terminals (on the sensor itself).
If the VAF sensor is good, then your multimeter should register an Ohms value that will smoothly increase as you open the measuring plate and decrease as you close it.
These are the test steps:
Disconnect the vane air flow sensor's connector.
Place the multimeter in Ohms (Ω) mode.
Connect the multimeter leads (with a suitable tool) to the male spade terminals of the sensor that correspond to: Circuit Number 3 and Circuit Number 6.
Manually open and close the sensor's measuring plate (vane) as you watch the Ohms readings on the multimeter.
The range of the resistance (Ω) will be anywhere in the vicinity of 20 Ohms with the plate fully closed to 1000 Ohms with the plate fully open.
Repeat this as often as you need to verify that the numbers on the multimeter decrease or rise smoothly every single time and without any gaps.
Let's interpret your multimeter test result:
CASE 1: The Ohms value increased/decreased as you opened/closed the measuring plate (vane) and without gaps (in the reading). This is the correct test result.
You can conclude that your 1988-1992 2.2L Mazda 626's VAF sensor is NOT defective if you have confirmed it's getting power, Ground, and that the Ohms value increased/decreased as indicated in this test section.
CASE 2: The Ohms value DID NOT increase/decrease as you opened/closed the measuring plate (vane) as indicated in the test instructions. This test result tells you that the VAF sensor is defective.
TEST 4: Testing The VAF Signal With The Engine Running
In this test section we're gonna' see if the VAF sensor is creating a voltage signal that increases as we rev the engine up.
It's important that before you start the test, the engine in your Mazda should be at its normal operating temperature. You'll be using the voltage reading you'll obtain at idle as a base to diagnose the VAF sensor.
If the VAF sensor is defective, it will produce a voltage signal that'll stay stuck in one value as you rev the engine up or a value that increases but has gaps.
IMPORTANT: The VAF sensor must remain connected to its electrical connector to perform this test. For this reason you'll need to use a back probe or a wire-piercing probe. You can see an example of this tool here: Wire Piercing Probe.
OK, let's get started:
Connect the red multimeter test lead to the Number 6 wire as shown in the photo. This is the red with black stripe wire.
Place the multimeter in Volts DC mode and connect the black multimeter test lead to the battery negative (-) terminal.
Start the already warmed up engine.
Note the voltage reading on your multimeter at idle. This reading may be stable (with only small fluctuations) or unstable with very extreme fluctuations. No matter what the instability in the reading, this will be your base reading.
Accelerate the engine as you watch the multimeter's voltage readings.
This voltage should INCREASE every time the engine is accelerated.
Repeat this as often as you need to verify that the voltage numbers on the multimeter INCREASE smoothly every single time.
If the VAF sensor is good, the voltage reading will increase/decrease as you rev up/rev down the engine.
Let's analyze your VAF signal test result:
CASE 1: The voltage signal increase/decrease as you accelerated/decelerated the engine. This is the correct test result and let's you know that the vane air flow meter is working OK.
CASE 2: The voltage signal DID NOT increase/decrease as you accelerated/decelerated the engine. This test result let's you know that the vane air flow meter is defective.
If this info really saved the day, buy me a beer!