How To Test The Oxygen Sensor (1991-1994 1.5L Honda Civic)

The single wire oxygen sensor, on the 1991-1994 1.5L Honda Civics, can easily be tested using only a multimeter. This multimeter test can tell you if it has failed or not and all without having to remove it from its place on the exhaust manifold.

In this tutorial, I'll show you how in a step-by-step way.

NOTE: This tutorial applies to the single wire oxygen sensor equipped 1.5L Honda Civic. If your Honda Civic has a 4 wire oxygen sensor, then the testing procedures in this tutorial do not apply to it. See the box titled Applies To: on the right column for 1.5L Honda Civic application specifics.

You can find this tutorial in Spanish here: Cómo Probar El Sensor de Oxígeno (1.5L Honda Civic) (at: autotecnico-online.com).

Symptoms Of A Bad Oxygen Sensor

The fuel injection computer in your Honda needs to know if it's injecting too much or not enough gasoline into the engine. Why? So that it can adjust the air/fuel mixture that the engine needs to burn to create power, get good fuel economy, and pollute less.

The main component it uses to control (fine-tune) the air fuel mixture is the single wire oxygen sensor that's located before the catalytic converter (your Civic only uses one oxygen sensor). Since the feedback information that the O2 sensor provides is so important, your Honda is going to perform poorly when it fails.

The effects of a bad oxygen sensor can be very subtle since they usually do not cause serious drive-ability problems. Here are the most common symptoms:

• O2 sensor will stay stuck reporting a false rich air/fuel mixture.
• O2 sensor will stay stuck reporting a false lean air/fuel mixture.
• O2 sensor will respond to slowly to changes in the air/fuel mixture being burned in the engine.
• The check engine light (CEL) will be shining nice and bright to let you know there's a problem.
• One of the following diagnostic trouble codes registered in the computer's memory:
  • Code 1 Oxygen Sensor Circuit.
• Really bad gas mileage.
• Won't pass state mandated emission testing.

Where To Buy The O2 Sensor And Save

You can buy the single-wire oxygen sensor for your 1.5L Honda Civic using the following links:

Not sure if the above oxygen sensor fits your particular 1.5L Honda Civic? Don't worry. Once you get to the site, they'll make sure it does. If it doesn't, they'll find the one that does by asking you the specifics of your Civic.

TEST 1: Checking The O2 Signal With A Multimeter

As mentioned in the previous section, the single wire O2 sensor will fail in one of 3 ways. It'll stay stuck reporting a rich condition, or stay stuck reporting a lean condition, or respond too slowly to changes in the air/fuel mixture. If the terms ‘rich’ and ‘lean’ aren't familiar to you, take a look at the section Oxygen Sensor Basics for more info.

You and I can see what the oxygen sensor is reporting by tapping into its signal wire with a multimeter. So, for our first test, we're gonna' see what the O2 sensor is reporting and determine if there's a problem or not.

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 recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing (at: easyautodiagnostics.com).

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 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 is the correct test result since it shows the oxygen sensor reacting and reporting the lean and rich conditions the fuel injection computer is creating and compensating.

There's a good chance that even tho' the voltage is moving up and down (as it should), the O2 sensor is reacting too slowly. So, my suggestion is to see how fast it responds to a rich air/fuel mixture. If it responds too slowly, the sensor needs to be replaced. For this test go to: TEST 2: Manually Creating A Rich Condition To Test The O2 Sensor.

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.