How To Test The Front Oxygen Sensor With A Multimeter (1.6L Toyota Corolla)

The front oxygen sensor is a 2 wire type which means it doesn't have an internal heater to worry about.

You can easily find out if the oxygen sensor is bad or just plain worn out with a simple multimeter test. In this tutorial I'll show you how to

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 Toyota 1.6L Tutorials.

Symptoms Of A Bad Oxygen Sensor

The fuel injection computer, on your 1.6L Toyota Corolla, needs to know if it's injecting too much or not enough fuel into the engine. The front oxygen sensor is tasked with this job by sensing the amount of oxygen in the exhaust stream and then reporting it to the computer.

When the fuel injection computer injects too much fuel, the exhaust (the O2 sensor is exposed to) becomes rich in hydrocarbons and low on oxygen. This is known as a rich condition. The O2 sensor responds by creating a voltage signal between .5 and 1 Volt DC.

When the computer does not inject enough fuel, the exhaust becomes lean in hydrocarbons and high on oxygen (this is known as a lean condition). The O2 sensor responds by creating a voltage signal between .01 and .5 Volt DC.

When the O2 sensor fails or slows down (due to age) your vehicle's gas mileage suffers and your Corolla starts to pollute more. You'll also see one or more of the following symptoms:

  1. One of the following trouble codes lighting up the check engine light:
    1. P0130: Oxygen Sensor Circuit (Sensor 1).
    2. P0133: Oxygen Sensor Circuit (Sensor 1) Slow Response.
  2. Bad gas mileage.
  3. Not gonna' pass the smog check.

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 (at: easyautodiagnostics.com).

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 Front Oxygen Sensor With A Multimeter (1.6L Toyota Corolla)

To find out if the front O2 sensor is bad (or too slow that it's having an impact on your Corolla's gas mileage), we need to check its voltage signal output with a multimeter as we manually force a rich and lean condition.

Before we force these 2 conditions, we need to see what the front oxygen sensor is reporting. In other words: we need see if it's stuck reporting a rich, or a lean condition, or if it's working OK at the moment before we do anything to the air/fuel mixture.

OK, since your Toyota Corolla's front oxygen sensor has 2 wires... you'll notice that the engine wiring harness connector's wires are a black (BLK) one and a brown (BRN) one. The wire that you need to tap into for all 3 tests is the brown (BRN) one to be able to read the O2 sensor signal with your multimeter.

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 to the BRN wire of the front O2 sensor's engine wiring harness connector. 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 (at: easyautodiagnostics.com).

  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 .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.