How To Test a Honda Civic Oxygen Sensor

You have two different kinds of Civic Oxygen Sensor in your Honda. One is the upstream, or primary oxygen sensor that controls fuel delivery. This sensor is mounted in your exhaust header and sends an electronic signal to your Honda Civic ECU or Engine Control Unit.

The other type of Civic Oxygen Sensor is your downstream or secondary 02 sensor. This sensor is primarily responsible for making sure that your catalytic converter is working properly. This unit is mounted after your cat, and reads the exhaust gases to make sure that your catalytic converter is doing it’s job.

Today I will be showing you how to test your primary or front oxygen sensor in a 1996 Honda Civic. This vehicle is equipped with a 1.6 liter SOHC Honda engine, and you will need to use a digital multimeter to complete this guide.

This test is best performed when your engine is cold, to avoid being burned or injured during the test. Your Honda Civic header is made of cast iron, so it can retain heat for quite some time.

Where is my Civic Oxygen Sensor Located?

Depending on the year and the engine type ( VTEC or non-VTEC ) of your Civic, your primary 02 sensor location will differ. Some models will have it mounted to the top of the collector, as shown in this image of a 1999 Honda Civic SOHC engine below.

Older models will place the primary 02 sensor further down the collector and header system. Our test vehicle is a 1996 Honda Civic, as shown in the image below.

Either way finding the 02 sensor connector and disconnecting it is easy to do. Once you’ve found the 02 wiring connector and disconnected it you can begin our how to test tutorial.

Symptoms of a failed Civic Oxygen Sensor

When your primary 02 sensor goes out your SOHC Civic is going to have a hard time running right. You may experience idle issues and lack of power, as well as hesitation and trouble with your transmission shifting right.

This happens because your ECU or Engine Control Unit doesn’t know how rich or lean your engine is running. When this occurs your idle will rise artificially because your engine will run overly rich. Here’s some other symptoms of a bad 02 sensor.

• Bad fuel economy
• Trouble with transmission – harsh shifting, inconsistent shift points
• High idle
• Premature catalytic converter failure
• Check Engine Light ON

If this condition is left uncorrected, the excessive hydrocarbons in your exhaust stream will cause your catalytic converter to burn out. This is an expensive repair and one that can be avoided by simply performing this How To test.

Testing the Civic Oxygen Sensor for Power

The first part of our test will be checking your primary 02 sensor for power signal. In order to test this you need to insert your Civic key and turn it to the “ON” position. This powers the sensors in your engine bay, but do not start your car.

Using your digital multimeter, you will need to probe the ENGINE side of the harness at PIN C as shown. The Civic oxygen sensor diagram as shown is the SENSOR side, so make sure to use this schematic as a reference only. The wire at PIN C is a BLACK wire with a YELLOW stripe.

If you have power here at this wire, great the next thing to test is your heater element ground. This wire is PIN D or the BLACK wire with a WHITE stripe on the ENGINE harness.

The last leg of this test is to check the sensor ground which is PIN B. The wire on the ENGINE side of the harness for this pin is a GREEN wire with a BLACK stripe. The last wire is the primary 02 sensor signal, which is PIN A. This wire is WHITE on the ENGINE harness, although if you have the right signals at pins B, C and D chances are your front Civic 02 sensor is dead.

Remember that you are working on the ENGINE side of the harness for this step, and our diagram is the SENSOR side.

Testing the internal resistance of your Honda Civic 02 Sensor

Now that you know your Honda Civic primary oxygen sensor is getting power and ground, the last step is to measure the internal resistance. Turn your multimeter to the OHMS position and you will be measuring the SENSOR side of the harness.

Put both probes to PIN C and PIN D to read the internal resistance of your Civic oxygen sensor. If your upstream sensor is still in good condition, you should see between 10-40 Ω. 

If your upstream 02 sensor doesn’t return these values, it’s time to replace it.

Replace your front Civic Oxygen Sensor with the proper replacement 02 sensor. Use a OBDII scan tool to clear your check engine light and you are set! Have any questions regarding our Civic Oxygen Sensor tutorial? Leave them for us below and let us know.