The idea of testing the MAF sensor can seem a bit overwhelming, but the test isn't difficult to perform and just a few basic tools are all that's required for the test.
I'll walk you through the process step by step in this tutorial. With the result of your test, you'll have a clear picture of the condition of the MAF sensor - whether it is working or not.
NOTE: This is an ON CAR test -no need to remove the MAF sensor from its place to test it.
Contents of this tutorial:
- Common Symptoms Of A Bad MAF Sensor.
- What Tools Do I Need?
- Circuit Descriptions Of The MAF Sensor Connector.
- Where To Buy The MAF Sensor And Save.
- How Does The MAF Sensor Work?
- TEST 1: Making Sure The MAF Sensor Is Getting 12 Volts.
- TEST 2: Making Sure The MAF Sensor Is Getting Ground.
- TEST 3: Testing The MAF Signal With A Multimeter.
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Common Symptoms Of A Bad MAF Sensor
The fuel injection computer needs to know how much air is entering the engine so it can calculate the correct amount of fuel to inject into the cylinders.
As you guessed it, the component responsible for measuring airflow into the engine is the MAF sensor.
Sooner or later, the mass air flow sensor will fail, and as it is a critical component of the engine management system, one or more of the following symptoms will occur when it fails:
The check engine light will illuminate and one of the following trouble codes will be stored in the computer's memory:
- P0101: MAF Sensor Performance Problem.
- P0102: MAF Sensor Circuit Low Frequency Signal.
- P0103: MAF Sensor Circuit High Frequency Signal.
You'll also see one or more of the following symptoms:
- Check engine light illuminated on your instrument cluster.
- Lack of power when accelerating the engine/vehicle.
- Black smoke coming out of the tailpipe.
- Bad gas mileage.
- Engine idles rough.
- Engine starts but immediately stalls.
- Extended engine cranking. In other words, you've got to crank the engine a long time for it start.
What Tools Do I Need?
The most important tool you'll need to diagnose a mass air flow sensor is a multimeter that can read Hertz frequency. Not all multimeters can do this.
Apart from a Hertz-capable multimeter, you'll need one or more of the following tools:
- A multimeter that can read Hertz frequency. If you don't have one and would like to buy one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
- A wire piercing probe or a back probe to be able to access the signal within the MAF sensor's output signal wire. To see what this tool looks like, click here: Wire Piercing Probe.
- Although not an absolute must, a code reader or a scan tool to be able to extract any codes registered in the fuel injection computer's memory.
As you can see, there's nothing in the list above that will break the bank!
Circuit Descriptions Of The MAF Sensor Connector
The MAF sensor has three wires coming out of its connector. The following table has a brief description of each:
|A||Yellow (YEL)||MAF Signal|
|B||Black with white stripe (BLK/WHT)||Ground|
|C||Pink (PNK)||12 Volts DC|
To test the MAF signal circuit, I recommend you use a wire-piercing probe or a back probe. You can see what this tool looks like here: Wire Piercing Probe.
IMPORTANT: All of the tests are ON CAR TESTS, do not remove the mass airflow sensor from the vehicle or its plumbing.
Where To Buy The MAF Sensor And Save
How Does The MAF Sensor Work?
As previously mentioned, the role of the MAF sensor in the engine management system is to measure the amount of air entering the engine. Here are more specific details on how it gets the job done:
- When you turn the key to start the engine, the pink (PNK) wire supplies 12 Volts to the MAF sensor.
- The black with white stripe (BLK/WHT) wire supplies chassis Ground.
- As soon as the engine starts and air starts flowing through the MAF sensor, the yellow (YEL) wire transmits the frequency signal generated by the MAF sensor to the fuel injection computer.
- An increase in engine RPM, such as when you press the accelerator pedal, will result in a corresponding increase in the Hertz frequency signal from the MAF sensor.
- Conversely, when you release the accelerator pedal and the engine RPM decreases, the Hertz signal from the MAF will decrease as well.
When the MAF sensor fails, it'll usually always stay stuck, producing a single Hertz frequency value or none at all when engine RPM increase or decrease.
TEST 1: Making Sure The MAF Sensor Is Getting 12 Volts
The MAF sensor requires power in the form of 10 to 12 Volts, without which it cannot generate its signal.
To get the our MAF sensor testing started, we'll make sure the MAF sensor has power.
The pink (PNK) wire of the MAF sensor is the one responsible for supplying power to the MAF sensor.
In the image above of the 3-wire MAF sensor connector, the PNK wire connects to the terminal I've marked with the letter A so you can easily locate it.
We'll do an easy multimeter test (in Volts DC mode) to quickly determine if the PNK wire is delivering power to the MAF sensor.
IMPORTANT: If you probe the front of the female terminal (of the connector), be careful not to damage it, or you'll need to replace the connector with a new one.
These are the test steps:
Put the multimeter in Volts DC mode.
Disconnect the MAF sensor from its electrical connector.
With the red multimeter test lead and an appropriate tool, probe the terminal labeled with the letter C.
CAUTION: When probing the front of the female terminal, be careful not to damage it with the multimeter test lead.
Connect the black multimeter test lead to the battery negative (-) terminal.
Turn key to the ON position but don't crank or start the engine.
You should see 10 to 12 Volts on the multimeter.
Let's take a look at what your test results mean:
CASE 1: The multimeter registered 10 to 12 Volts. This is the correct and expected test result and it confirms that the MAF sensor is receiving power.
The next step is to make sure that the MAF sensor is getting Ground. For this test go to: TEST 2: Making Sure The MAF Sensor Is Getting Ground.
CASE 2: The multimeter DID NOT register 10 to 12 Volts. This test result lets you know that the mass airflow sensor isn't getting power. Without power, it will not function.
Your next step is to find out why this voltage is missing and resolve the problem.
Once you've restored power to the wire, your MAF sensor should function again.