Testing The Front Oxygen Sensor (1995-2000 1.6L Honda Civic)

When the upstream oxygen sensor fails (commonly known as O2S11) on your OBD II equipped 1.6L Honda vehicle, you're gonna' see the check engine light lit up on your instrument cluster.

Not only that, you're gonna' spend a little more money at the pump since the your car won't get the same gas mileage it did before it failed.

Thankfully, the O2 sensor can be tested, before it's replaced, and in this article I'll show you how.

You can find this tutorial in Spanish here: Cómo Probar El Sensor De Oxígeno (1.6L Honda Civic) (at: autotecnico-online.com).

Important Suggestions And Tips

TIP 1: The info in this tutorial will help you to test the oxygen sensing performance of the front oxygen sensor. You won't find any info on how to test the front O2 sensor's heater or trouble code P0135. For the testing procedures of the front O2 sensor's heater, see this tutorial: How To Test Trouble Code P0135 (1995-2000 Honda 1.6L).

TIP 2: The test info in this article can only be applied if you have a scan tool. This scan tool must have Live Data capability.

You don't need the Honda factory scan tool or an expensive professional technician level scan tool to follow the test procedures in this article, since a simple generic scan tool will do just fine (Don't have a scan tool? Need a scan tool? check out my recommendation: Actron CP9580 Scan Tool).

TIP 3: The oxygen sensor test described in this tutorial is an on-car test, so you do not need to remove it to test it.

Symptoms Of A Bad Oxygen Sensor

The fuel injection computer in your Honda is constantly adjusting 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 upstream 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:

• The O2 sensor will stay stuck reporting one voltage value as the engine runs (instead of producing a voltage that moves between 0.100 and 0.900 Volts).
  • It will stay stuck below 0.500 Volts. Reporting a never-ending lean condition.
  • It will stay stuck above 0.500 Volts. Reporting a never-ending rich condition.
• O2 sensor reacts to slowly to changes in the air/fuel mixture.
• 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 PCM's memory:
  • P0131 Upstream Heated Oxygen Sensor (O2S11) Circuit Out Of Range Low Voltage (Bank 1).
  • P0133 Upstream Heated Oxygen Sensor (O2S11) Circuit Slow Response (Bank 1).
• Really bad gas mileage.
• Won't pass state mandated emission testing.

TEST 1: Checking The O2 Signal With A Scan Tool

The very first thing we need to do, after confirming that the check engine light (CEL) is lit up by oxygen sensor performance trouble codes, is see what the oxygen sensor is doing with the engine running.

This will tell us if: It's stuck reporting a rich condition, or stuck reporting a lean condition, or it's responding 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 connecting a scan tool with live data capability and seeing what the O2S11 PID is reporting.

NOTE: If you don't have a scan with live data capability and need a recommendation, take a look at this review: Actron CP9580 Scan Tool.

These are the test steps:

1. 1

   Connect your scan tool and go to its live data function. If you're testing the front O2 sensor, go to the PID labeled: O2S11.

2. 2

   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.

3. 3

   Observe the voltage changes on the scanner 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. You'll be able to see these voltage changes on your scan tool.

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.