In this article, I'll show you how to test the mass air flow (MAF) sensor on your GM 3.8L (3800) vehicle without a scan tool.
Now, in case you wondering if this test applies to your specific vehicle, this article covers the MAF sensor on 1996 thru' 2005 3.8L V6 Buick, Chevrolet, Oldsmobile, Pontiac 3.8L V6 equipped cars. For more specific application info, take a look at the box titled Applies To: on the right column.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar El Sensor MAF GM 3.8L (1996-2005) (at: autotecnico-online.com).
If you need to just clean the MAF sensor, you can find this article here: Cleaning The MAF Sensor (at: troubleshootmyvehicle.com). There are also several other MAF sensor test article I've written you might be interested in looking at:
- How To Test The MAF Sensor on 3.1L, 3.3L, and 3.8L Buick, Oldsmobile, Pontiac (1988-1996)
- How To Test The GM Mass Air Flow Sensor (Early Type): Buick, Chevy, Olds, Pontiac 3.1L, 3.4L, 4.3L, 5.0L, 5.7L V6 Engines (1996-2005)
- How To Test The GM Mass Air Flow (MAF) Sensor: 4.8L, 5.3L, 6.0L, and 8.1L V8 Engines (1999-2010)
- How To Test The GM Mass Air Flow Sensor: GMC Savana Van and Chevy Express Van 4.3L, 5.3L, 6.0L Engines (2003-2008)
Common Symptoms Of A Bad GM MAF Sensor
This list covers the majority of symptoms I've seen on these types of GM mass air flow sensors:
- MAF codes that light up the check engine light (CEL) on your instrument cluster.
- P0101 Mass Air Flow System Performance.
- P0102 Mass Air Flow Low Frequency.
- P0103 Mass Air Flow High Frequency.
- MAF sensor malfunction that DOES NOT light up the check engine light (CEL).
- Lean and/or Rich code(s).
- Fuel Trim code(s).
- A tremendous lack of power upon acceleration.
- Black smoke coming from the tail-pipe.
- Bad gas mileage.
- Vehicle may idle rough and stall.
What Tools Do I Need?
As I mentioned at the beginning, you don't need a scan tool to follow the tests in this article, but you do need a multimeter.
This multimeter has to be a digital multimeter that can read high Hertz (Hz) Frequency (don't have a digital multimeter that can read Hertz frequency? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing).
One other tool, that I recommend, is for you to use a wire-piercing probe to to test the signal of each wire (to see what this tool looks like, click here: Wire-Piercing Probe.
Circuit Descriptions Of The GM MAF Sensor Connector
As you're already aware, the MAF sensor on your vehicle is a 3 wire sensor.
Whether you're driving a Buick, Chevy, Olds, or Pontiac vehicle (with a 3.8L V6) the circuits descriptions of the wires coming out of the Mass Air Flow (MAF) sensor are the same.
You'll notice that the photo above, I have the MAF connectors lettered A thru' C (if you look closely at the MAF sensor itself, you'll see these letters on it too). I'll be using these letters for the circuit descriptions. Here's the description of each circuit below:
- Letter A:
- MAF Signal.
- Letter B:
- Ground.
- Letter C:
- Power (12 Volts).
The one circuit that has to be tested with the connector connected to the MAF sensor is circuit A. This is the one that delivers the MAF signal that the MAF sensor creates to the PCM. The best way to get to this signal, inside the wire, is to use a wire piercing probe.
How Does The MAF Sensor Work?
The MAF sensor's job is to measure the amount of air that the engine is breathing. This measurement is accomplished by the sensor's two Hot Wires that are exposed to the incoming air.
The electronics inside the MAF sensor then convert this measurement of the airflow (as sensed by the two Hot Wires) into a high frequency digital signal. This signal can be measured with a digital multimeter that can read Hertz frequency or with an oscilloscope.
So, keeping this in mind, it's a given that the engine will breathe in more air at, let's say, 2,500 RPMs than when it's sitting at an idle of 900 RPMs and of course the Hertz reading will be higher at 2,500 RPMs than at 900 RPMs.
When testing this Hz frequency signal, the important thing to know is not an actual Hz frequency number at a specific RPM, but to look for crazy and extreme fluctuations in the Hz frequency signal that do not correspond to the actual air intake (RPMs) of the engine or NO SIGNAL AT ALL. In the TEST 3 section of this article, I'll show how you'll use a base Hz reading at idle from the MAF sensor that will help you to confirm that the MAF sensor is bad or not.
The MAF sensor test consists of verifying that the MAF sensor is receiving 12 Volts, Ground, and that it is indeed producing a correct MAF signal. This is an on-car test. Testing for these three signals is easy and I'll take you step by step thru' the whole test.
TEST 1: Testing The MAF Signal
For our first test, we'll check the MAF signal coming out of the sensor and going to the ECM.
The wire that we're gonna' tap into, to check the MAF signal, is the wire labeled with the letter A in the photo above.
Before you start the MAF signal test, start the engine and let it reach it's normal operating temperature.
NOTE: The MAF sensor must be connected to its connector to perform this test. You'll need to back probe the MAF signal wire at the connector or use a wire piercing probe on the wire. You can see an example of this tool here: Wire-Piercing Probe.
Let's get going:
- 1
Place your multimeter in frequency (Hz) mode.
- 2
With a suitable tool connected to the red multimeter test lead, probe the A circuit as shown in the photo.
- 3
Connect the black multimeter test lead to the battery negative (-) terminal.
- 4
Start the already warmed up engine.
- 5
Note the Hertz 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.
- 6
Manually accelerate the engine from the engine compartment as you watch the multimeter's frequency readings. The Hertz frequency readings should increase as you rev up the engine.
- 7
Let go off of the throttle and let the engine returns to idle. The Hertz reading should come down to the base Hertz reading you observed in step 5 of this test.
- 8
Rev up/down the engine several times. Each time the multimeter should register an increase/decrease in the MAF signal voltage.
Let's analyze your MAF signal test result:
CASE 1: The Hertz value increased/decreased as you revved up/down the engine. This test result lets you know that the MAF is OK and therefore functioning correctly.
CASE 2: The Hertz value DID NOT increase/decrease as you revved up/down the engine. This test result usually tells you that the MAF is bad.
To be sure the MAF sensor is bad, we need to make sure its getting power and Ground. For the first of these two tests, go to: TEST 2: Testing The Power (12 Volts) Circuit.
