How to Test the Oxygen Sensor With a Multimeter (2.8L V6 S10/S15)

The oxygen sensor, on your OBD I 2.8L V6 equipped Chevy S10 (or GMC s15) is a single wire type that can be easily tested with a multimeter. You don't need a professional technician level scan tool to do it.

In this tutorial I'll show you how in a step-by-step way and in plain English!

Contents of this tutorial at a quick glance:

  1. Symptoms of a Bad Oxygen Sensor.
  2. Important Tips and Suggestions.
  3. TEST 1: Checking the O2 Signal With a Multimeter.
  4. TEST 2: Manually Creating a Rich Condition to Test the O2 Sensor.
  5. TEST 3: Manually Creating a Lean Condition to Test the O2 Sensor.
  6. Where to Buy the O2 Sensor and Save.
  7. More GM 2.8L Tutorials.

En Español Puedes encontrar este tutorial en Español aquí: Cómo Probar El Sensor De Oxígeno (2.8L V6 GM) (en: autotecnico-online.com).

Symptoms Of A Bad Oxygen Sensor

In a nutshell, the fuel injection computer, on your S10/S15, uses the oxygen sensor to adjust injector pulse width.

In more technical terms, the O2 sensor has a pretty direct impact on the air/fuel mixture adjustments the computer makes.

For example, if the O2 sensor reports a rich condition, the PCM injects less fuel. If the O2 sensor reports a lean condition, the PCM injects more fuel.

So, when the O2 sensor fails... you'll see one or more of the following symptoms:

  1. Trouble codes illuminating the check engine light (CEL):
    1. Code 13: Oxygen (O2) Sensor Circuit.
    2. Code 44: Lean Exhaust.
    3. Code 45: Rich Exhaust.
  2. Bad gas mileage.

NOTE: If you'd like a more detailed explaination of how the O2 sensor works, take a look at this tutorial on the sister-website to this one: Oxygen Sensor Basics (at: troubleshootmyvehicle.com).

Important Tips And Suggestions

TIP 1: You need to use a 10 megohm impedance digital multimeter to test the oxygen sensor using the test described in this tutorial. Using a multimeter that's not rated a 10 megohm impedance multimeter will damage the oxygen sensor. If you don't own one, take a look at the following recommendations here: Buying a Digital Multimeter for Automotive Diagnostic Testing

TIP 2: Be careful and take all necessary safety precautions. The oxygen sensor and the exhaust manifold it's bolted into get and stay very hot! Be careful and don't touch the O2 sensor or the exhaust manifold for any reason once the engine is running or is cooling down.

TIP 3: Set up your multimeter connections with a cold engine. This will ensure that you avoid getting burned from hot exhaust or engine components.

TEST 1: Checking The O2 Signal With a Multimeter

How to Test the Oxygen Sensor With a Multimeter (2.8L V6 S10/S15)

The voltage signal that the O2 sensor creates is a direct result of the reaction to the oxygen content of the exhaust it's exposed to.

The more fuel in the exhaust, the less oxygen in the exhaust the higher the voltage signal the O2 sensor produces.

The less fuel in the exhaust, the more oxygen in the exhaust the lower the voltage signal the O2 sensor produces.

IMPORTANT: Use a 10 megohm impedance digital multimeter to test the O2 sensor. If you don't own one, take a look at the following recomendations here: Buying a Digital Multimeter for Automotive Diagnostic Testing

These are the test steps:

  1. 1

    Set your multimeter to Volts DC mode. Remember, your multimeter must be a 10 megohm impedance type.

  2. 2

    Connect your multimeter to oxygen sensor wire. You'll need to use a wire piercing probe to accomplish this.

    To see what a wire piercing probe looks like and where to buy it, look here: Wire Piercing Probe Tool.

  3. 3

    Start the engine and let it warm up till it reaches normal operating temperature.

    If the engine is completely cold, accelerate it to about 2,000 RPMs for about 5 minutes till the upper radiator hose starts to get warm to the touch.

  4. 4

    Observe the multimeter voltage changes once the engine has reached normal operating temperature and you have let it return to its normal idle RPM.

    If the O2 sensor is OK, then it will produce a constantly changing voltage between .4 to 1 Volt DC the entire time the engine is running.

Let's take a look at what your test results mean:

CASE 1: The O2 sensor signal voltage moved up and down the as the engine idled. This tells you that the O2 sensor is working and NOT defective.

CASE 2: The O2 sensor voltage was stuck above .5 Volts as the engine idled. This test result tells you that the O2 sensor is seeing a constant rich air/fuel mixture. This could be a result of an engine performance issue or the O2 sensor could be bad.

To find out, the next step is to create a lean air/fuel mixture to see if the O2 sensor reacts to it. For this test go to: TEST 3: Manually Creating a Lean Condition to Test the O2 Sensor.

CASE 3: The O2 sensor voltage was stuck below .5 Volts as the engine idled. This test result tells you that the O2 sensor is seeing a constant lean air/fuel mixture. This could be a result of an engine performance issue or the O2 sensor could be bad.

To find out, the next step is to create a rich air/fuel mixture to see if the O2 sensor reacts to it. For this test go to: TEST 2: Manually Creating a Rich Condition to Test the O2 Sensor.