Testing to see if the mass air flow (MAF) sensor on your Toyota 1.8L equipped Corolla is bad (or not) isn't hard.
In this tutorial, I'm gonna' show you how to do it with just a multimeter and in step-by-step manner.
This tutorial covers 4 different 1.8L equipped Toyota models. To find out if this tutorial applies to you specific vehicle, take a look at the box titled: ‘Applies To:’ on the column on the right.
To help you navigate this article, here are its main points:
- Symptoms Of A BAD MAF Sensor.
- What Tools Do I Need To Test The MAF Sensor?
- What Does The MAF Sensor Do?
- TEST 1: Checking The MAF Sensor Power Circuit.
- TEST 2: Checking The MAF Sensor Ground Circuit.
- TEST 3: Checking The MAF Sensor Signal.
You can find this tutorial in Spanish here: Cómo Probar El Sensor MAF (1.8L Toyota Corolla) (at: autotecnico-online.com).
Symptoms Of A BAD MAF Sensor
The MAF sensor's job is to measure the amount of air entering the engine (when the engine is running) and transmit this info to your Toyota's fuel injection computer. The computer then uses this air flow measurement, along with other sensor inputs, to inject the correct amount of fuel into the engine.
So when the MAF sensor goes BAD, you'll get the check engine light to shine nice and bright on your Instrument Cluster.
You'll also see one or several of the following symptoms of a BAD MAF sensor:
- Diagnostic trouble codes:
- P0101: Mass Air Flow (MAF) Sensor System Performance
- P0102: Mass Air Flow (MAF) Sensor Circuit Low Input.
- P0103: Mass Air Flow (MAF) Sensor Circuit High Input.
- BAD gas mileage.
- Rough idle.
- Lack of power on acceleration.
- Black smoke coming out of the tailpipe.
- Won't pass the emissions test.
It's rare for the mass air flow (MAF) Sensor to go BAD and not leave a diagnostic trouble code... but sometimes you'll get the MAF trouble code and the MAF is good. So, it's always a good idea to test it.
What Tools Do I Need To Test The MAF Sensor?
The cool thing about testing the MAF sensor on your Toyota is that you don't need any expensive or exotic tools. Here's a basic list of tools you'll need:
- A multimeter.
- If you need to upgrade or buy a multimeter, check out my recommendation: Abe's Multimeter Recommendation (found at: easyautodiagnostics.com).
- Wire piercing probe.
- Although this tool is not an absolute must, if you do buy one, you'll realize just how easy it makes testing the voltages inside the wires.
- If you need to see what this tool looks like, you can see it here: Wire Piercing Probe.
A scan tool comes in handy... but you won't need it to use the testing info in this article.
What Does The MAF Sensor Do?
The MAF sensor is tasked with measuring the amount of air entering the engine at any given RPM. The PCM (Powertrain Control Module = Fuel Injection Computer) then uses this measurement of air flow to inject the correct amount of fuel.
To get into more specifics: The MAF sensor informs the PCM the amount of air flow entering the engine by converting the measurement of air into a voltage signal that increases with more air flow (as you accelerate the engine) or decreases as the engine breathes less air.
This is the key to understanding how to MAF sensor works and how to test it. I'll repeat it once more: The more air the engine breathes, the bigger the voltage signal the MAF sensor creates. The less air the engine breathes, the smaller the voltage signal the MAF sensor sends the PCM.
Here's what it looks like on a multimeter:
- At an idle under 1000 RPM's the MAF sensor outputs about 1.1 Volts DC.
- At about 1500 RPM's the math signal output is about 1.2 volts DC.
- Ask about 3000 RPM's the MAF signal output is about 1.7 volts DC.
Remember, the important thing to know, is that at higher RPMs, when the engine is breathing more air, the MAF signal (in voltage) is greater than when the engine is idling.
Now, in testing the MAF sensor, you won't be looking for a specific voltage number at a specific RPM... but for crazy fluctuations in the signal that don't correspond to the amount of air entering the engine or NO SIGNAL AT ALL.
These are the circuit descriptions of the mass air flow (MAF) sensor
|MAF Sensor Connector Pin Out|
|1||Black||Fused power (12 Volts)|
|2||Blue w/ White stripe||MAF sensor ground (PCM)|
|3||Green||MAF sensor signal|
|4||Yellow w/ Black stripe||Intake Air Temp (IAT) Sensor|
|5||Brown||Intake Air Temp (IAT) Sensor|
As you’re probably already aware, the MAF sensor on your Toyota has 5 wires coming out of it’s connector. We only need to be concerned with three of the five wires... since the other 2 belong to the intake air temperature (IAT) sensor that is part of the MAF sensor assembly.
Let's turn the page and get testing...