TEST 3: Checking The MAF Sensor Signal
If you've reached this point, then you've confirmed that your Toyota's MAF sensor is being fed with both power and Ground.
The next step is to test your MAF sensor in action and see if it's producing a viable MAF sensor signal.
The wire that delivers this MAF voltage signal (to the PCM) is the one labeled with the number 3 in the photo above.
NOTE: Your Toyota's MAF sensor must remain connected to its electrical connector to be able to read the MAF signal (it produces). To access the signal in the wire, you'll need to use a back probe or a wiring piercing probe. You can see an example of this tool here: Wire Piercing Probe.
This what you'll need to do:
Place your multimeter in Volts DC mode.
Connect the red multimeter test lead to the wire labeled with the #3 in the photo above.
Connect the black multimeter test lead to the negative (-) battery terminal.
Start the engine and let it idle for a few minutes.
Your multimeter should read about 1.1 Volts DC at idle.
Accelerate the engine as you observer the voltage reading on your multimeter.
The voltage reading should increase as the engine's RPM increase and should decrease when you let go of the throttle. Generally, you'll see about 1.7 Volts DC at 3,000 RPM.
Let's interpret your MAF signal test results:
CASE 1: The multimeter registered the indicated voltage values when you accelerated and decelerated the engine. This is the correct and expected test result and tells you that the mass air flow (MAF) sensor is good.
If the mass air flow (MAF) sensor were bad, the voltage would have not gone up or down as you revved the engine up and down.
There's no need to replace the MAF sensor, since this test confirms that it's functioning.
CASE 2: The multimeter DID NOT register the indicated voltage values when you accelerated and decelerated the engine. Make sure that you're testing the correct wire, that your connections are OK, and repeat the test.
If you still don't see the voltage values going up when you accelerate the engine or go down when you decelerate the engine, then you've got a bad mass air flow (MAF) sensor on your hands.
Replace the MAF sensor.
MAF Test Summary
The key to successfully diagnosing your Toyota's mass air flow (MAF) sensor is knowing that as the RPM's go up, so does the voltage signal that the sensor reports to the PCM on the wire labeled with the number 3 (in the photos in the image viewer).
Also, when the MAF sensor on your Toyota fails, it usually fails in one of two ways:
- It'll stop producing a voltage signal, even tho' it's getting power and Ground.
- Or, it'll produce a signal but this signal won't go up or down as you accelerate or decelerate the engine.
I'm pointing this out, because you don't need to know a precise voltage number for a specific RPM. I know, I know... it would be great to have a specific value to compare against but trust me, you don't need it.
If in TEST 3, the voltage values went up and down... the MAF on your 1.8L equipped Toyota vehicle is OK.
If indeed the MAF sensor is fried on your vehicle, take a look at the MAF sensor offers below and compare. You just might save a few bucks.
More 1.8L Toyota Tutorials
You can find a complete list of 1.8L Toyota tutorial here: Toyota 1.8L Index Of Articles.
Here's a sample of the tutorials you'll find:
- How To Test For A Blown Head Gasket (Toyota 1.8L).
- How To Test Engine Compression (Toyota 1.8L).
- Misfire Codes: How To Troubleshoot And Repair Them (Toyota 1.8L).
- How To Test The Fuel Injectors (Toyota 1.8L).
If this info saved the day, buy me a beer!