How To Test The 1998 Volvo S70 MAF Sensor With A Multimeter

This tutorial will help you test the MAF sensor of the 1998 Volvo S70 using only a multimeter.

This MAF sensor test is easy and will accurately help you to find out if the MAF sensor is defective or not.

This tutorial was originally written in 2009 and has been updated.

You can find this tutorial in Spanish here: Cómo Probar El Sensor MAF De 1998 Volvo S70 (at: autotecnico-online.com).

Symptoms Of A Bad MAF Sensor

The most common symptoms of a bad MAF sensor are:

1. A MAF sensor code.
2. Lean and/or Rich code(s).
3. Fuel Trim code(s).
4. A tremendous lack of power upon acceleration.
5. Black smoke coming from the tail-pipe.
6. Vehicle may idle rough and stall.

Is Your Volvo's MAF Sensor Dirty?

The mass air flow test is a very easy and simple test but there are a couple of things that have to be done first.

The most important thing to do first, is to make sure your MAF sensor isn't contaminated with dirt and/or oil, since the tests in this article assume the MAF sensor isn't contaminated. Why? Because this MAF sensor is a hot-film type that easily becomes contaminated with dirt and stuff from the air filter not performing its job. Cleaning this type of sensor can be difficult since the heat-film is not clearly visible to the eye but it can be cleaned.

This contamination will cause the sensor to produce a lower reading to the ECM (Engine Control Module = Fuel Injection Computer). The most common symptom of this contamination is a hesitation or a time-lag in engine response that is felt after the accelerator pedal is depressed. As stated in the list at the beginning of this article, other symptoms may include but are not limited to: higher tailpipe emissions and diagnostic codes that may illuminate the "Check Engine" light.

If cleaning the MAF sensor, use an electronics spray cleaner to do it with. This in itself may solve your problem. Don't use carburetor or brake clean spray. These solvents can damage the sensor. Also, don't attempt to physically clean the sensor with anything. Check your local autoparts store, they will have MAF sensor cleaning spray.

After having checked for contamination the other things that you must check for (and eliminate if present) are:

1. That the engine does not have any vacuum leaks.
2. That there are no ignition system misfires. A misfire condition will skew the results of the test you'll perform here.

If the above conditions exist, repairing them first will more than likely solve your vehicle's drive-ability issue without having to test the MAF sensor, if not continue with the MAF Test in this article.

Circuit Descriptions Of The Volvo S70 MAF Sensor

The safest way to test these circuits, and the method I always use, is using a wire piercing probe (you can see an example of this tool here: Wire Piercing Tool). Using this probe, I don't have to disconnect the MAF sensor's connector to probe the front of the female terminal and possibly risk damaging it.

Independent of the method you use, be careful not to damage the wire or the female terminal. Take all safety precautions.

IMPORTANT: All of the tests are ON CAR TESTS, do not remove or disconnect the mass air flow sensor from the vehicle or from its plumbing.

As you've already noticed, the photo (above) has the MAF connector numbered 1 thru' 4. I'll be using these numbers for the circuit descriptions. The Sensor's connector itself has these numbers molded on it too. Here's the description of each circuit below.

• Number 1- Ground (chassis).
• Number 2- Ground 2. Provided by the ECM internally.
• Number 3- 12 Volt battery power.
• Number 4- MAF signal.

What about the color of the wires? Good question. The colors of the wires in the photo will not match what is on your vehicle. This is no cause for concern. The circuit descriptions are not tied to the color of the wire. In other words, no matter what the color of the wire, the circuit descriptions remain the same.

We're ready to get started.

The Volvo S70 MAF Sensor Test Basics

OK, you're gonna' start by checking the basics. These are 12 Volts and battery Ground to the MAF sensor. After that, we'll test the actual performance of the MAF sensor as the engine is running. Use a digital multimeter for all tests where a multimeter is called for.

The MAF sensor produces an analog voltage signal. This MAF signal's voltage is directly related to amount of air the engine is breathing. Common sense tells us that the engine will breathe in more air at 2500 RPMs than at an idle of 900 RPMs.

So keeping this in mind, the voltage value on the multimeter will be greater at 2500 RPMs than at 900 RPMs

Now, when testing this voltage signal, the important thing to know is not an actual Volts number at a specific RPM, but to look for crazy and extreme fluctuations in the voltage signal that do not correspond to the actual air intake (RPMs) of the engine. For example: If at idle the voltage reading starts to spike up and down without you accelerating the engine.

In the TEST 4 section of this article, I'll show how you'll use a base voltage reading at idle from the MAF sensor that will help you to confirm that the MAF sensor is bad or not.

Lastly, these tests are not designed to diagnose an intermittent problem with the MAF sensor. They are designed to diagnose a hard fault with the sensor.