Honda Civic P0135 Trouble Code – Test your O2 Sensor

The Honda Civic P0135 trouble code in your late model Honda signifies an issue with your oxygen sensor heater element. The specific code for the P0135 OBDII trouble code is Primary Heated Oxygen Sensor Heater Circuit Malfunction. It means there’s a problem with the heater element in your primary or front O2 sensor. Today I’ll be showing you how to test your front O2 sensor by using a digital multimeter in a 1996 Honda Civic EX. When the upstream O2 sensor fails on you, there’s a good chance that your Honda will run very poorly.

This is because your primary O2 sensor or oxygen sensor is also known as the EFI sensor. This sensor dictates the current air/fuel ratio in your exhaust stream to your engine computer or your ECU. Based on this signal the engine computer in your Honda Civic can control and adjust the delivery of fuel to your 1.6 liter SOHC engine. This can cause your engine to run rich which means too much fuel, or too lean, which means not enough fuel. When you see your Honda Civic check engine light on, you’ll need the right OBDII scan tool to pull out the stored Diagnostic Trouble Codes.

Symptoms of the Honda Civic P0135 check engine code

There’s quite a few problems with your Honda Civic when the P0135 OBDII trouble code is found. Some of these are listed below as the more common Honda Civic problems when your primary or upstream O2 sensor goes bad.

  • Bad gas mileage
  • Poor engine performance
  • Engine runs lean – possible engine damage
  • Engine runs rich – possible catalytic converter failure
  • Check Engine Light ON

Testing your Honda Civic Primary O2 Sensor

To begin testing the heater element of your upstream Honda Civic oxygen sensor, start by opening your Honda Civic hood. Then you will locate the four prong weatherproof Honda Civic O2 sensor connector that’s mounted near your radiator hose. This connector is mounted to a metal tab that can be freed by depressing the rear plastic tab. Once you have the connector removed, you can depress the locking tab to unplug the primary Civic oxygen sensor.

Honda Civic P0135 Trouble Code

The primary Honda Civic O2 sensor is located in the primary runners of the front exhaust manifold, or header system. As soon as you open the hood you should be able to see the sensor mounted in the exhaust. Now that you have your upstream Civic O2 sensor unplugged, you can refer to the Civic oxygen sensor wiring diagram below. Because the heater element in your upstream oxygen sensor has gone out, you’ll be testing the heater element primarily.

This wiring diagram refers to all Civics between the years of 1995-2000 with the 1.6L SOHC engine.

Honda Civic P0135 Trouble Code 1

Now don’t forget that you are testing the SENSOR side of your upstream Honda Civic oxygen sensor. This is a female spade and when you are testing it with your digital multimeter, don’t force the probes or leads into the sensor. Doing so could cause permanent damage or intermittent contact issues. Turn the dial of your multimeter to read resistance or OHMS, and gently probe the pins 3 and 4.

With your multimeter testing the primary O2 sensor, you should see an internal resistance between 10 to 40 Ω’s on your multimeter. This means that the internal heater element to your upstream oxygen sensor is working good. If you read an open condition or OL, or the resistance reads over 10,000 Ω your primary heater sensor has failed. If your sensor checks out but the Honda Civic P0135 trouble code remains, you’ll need to check the engine harness side of the wires.

Testing the Civic Oxygen Sensor Wiring


Now you can use the multimeter to make sure that your Honda Civic is sending the right signals through the engine harness. Refer to the chart below to read what the color of your Civic O2 sensor wires are, and their respective values.

You will start with the power wire which should be the BLACK wire with a YELLOW stripe in it. This is the wire that leads to PIN 3. If you have power there, check the ground circuit which is a BLACK wire with a WHITE stripe in it. This is the O2 sensor heater element ground signal. The other two wires are listed below, but typically are not related to the Honda Civic P0135 OBDII check engine light.

  • Pin 1 White Primary O2 Sensor Signal
  • Pin 2 Green with a Black Stripe – O2 Sensor Ground

Once you have the primary oxygen sensor wiring sorted and properly tested, you can use your OBDII scan tool to clear your check engine light. Have any questions regarding the Honda Civic P0135 Trouble Code? Leave us a comment below and let us know.

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