How To Test The Front Oxygen Sensor With A Multimeter (2.2L GM)

The front oxygen sensor on the 2.2L GM engines is a one-wire sensor, which means that it doesn't have an internal heater.

The oxygen sensor's performance can be easily tested with a multimeter. In other words, you don't need a scan tool with live data capability to see if the front oxygen sensor is working or not.

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

You can find this tutorial in Spanish here: Cómo Verificar el Sensor de Oxígeno con Multímetro (2.2L GM) (at: autotecnico-online.com).

Symptoms Of A Bad Oxygen Sensor

The PCM uses the oxygen sensor as a feedback sensor to find out if it's injecting too much or not enough fuel. Thus, a failed oxygen sensor has a direct impact on your vehicle's gas mileage and emissions.

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

• If OBD I equipped, you'll see one or more of the following trouble codes illuminating the check engine light (CEL):
  • Code 13: Oxygen (O2) Sensor Circuit.
  • Code 44: Lean Exhaust.
  • Code 45: Rich Exhaust.
• If OBD II equipped, you'll see one or more of the following trouble codes illuminating the check engine light (CEL):
  • P0131: Oxygen (O2) Sensor Circuit Low Voltage -Sensor 1.
  • P0132: Oxygen (O2) Sensor Circuit High Voltage -Sensor 1.
  • P0133: Oxygen (O2) Sensor Circuit Slow Response -Sensor 1.
  • P0135: Oxygen (O2) Sensor Circuit Insufficient Activity -Sensor 1.
• Bad gas mileage.
• Not gonna' pass the smog check.

NOTE: If you'd like a more detailed explanation 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: Your digital multimeter must be a 10 megohm impedance multimeter to test the oxygen sensor. 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.

Where To Buy The O2 Sensor And Save

The upstream single wire oxygen sensor in your 2.2L 4 cylinder equipped Cavalier (Sunfire, S10 or Sonoma) can be bought in any auto parts store, but I think you'll find the better price online. The following links are pretty good deals:

Not sure if the above oxygen sensor fit your particular 2.2L Cavalier (Sunfire, S10, Sonoma)? Don't worry, once you get to the site, they'll make sure it fits by asking you the specifics of your vehicle. If it doesn't fit, they'll find you the right one.

TEST 1: Checking The O2 Signal With A Multimeter

As you're already aware, the O2 sensor's job is to measure the amount of oxygen in the exhaust.

In nutshell, when the O2 sensor reports an exhaust with a high concentration of oxygen, it produces a low voltage signal (under 0.5 Volts). This high concentration of oxygen in the exhaust is identified as a 'lean' condition by the PCM.

When the concentration of oxygen is low, the oxygen sensor produces a high voltage signal (from 0.6 Volts to 1 Volts). The PCM then interprets this as a 'rich' condition.

You and I can create these rich and lean conditions to test the oxygen sensor. But before we do that, we first need to see what the oxygen sensor is reporting without us altering the air/fuel mixture (like we'll do in TEST 1 and TEST 3).

IMPORTANT: Use a 10 megohm impedance digital multimeter to test the O2 sensor.

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 4 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 0.4 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 0.5 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 0.5 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.