Oxygen Sensor Codes Keep Coming Back

There's a good chance that you have tested the O2 sensor on your Honda and it tested good or you replaced it, but it didn't solve the problem.

When this happens, it usually means that the problem (that's made us think the O2 sensor was bad) is being caused by something else. That something else is causing a rich or a lean condition that is causing the O2 sensor code.

Some of the things that can cause a rich condition are:

  • A cylinder misfire caused by:
    • Bad spark plugs.
    • Bad spark plug wires.
    • Bad distributor cap.
  • Clogged or leaking fuel injectors that are not atomizing the fuel correctly.
  • Bad fuel pressure regulator for leaking fuel into each vacuum hose.

Some of the things that can cause a lean condition are:

  • Vacuum leaks caused by:
    • Bad intake manifold gaskets.
    • Leaking or broken vacuum hoses.
    • Extremely clogged fuel filter.
    • Bad fuel pump that is not producing enough pressure or volume.

My suggestion to you is to take a good look at some of the above components and see what condition they're in or if they need to be tested before replacing any of them.

Oxygen Sensor Basics

The oxygen sensor's job is to report back to the PCM (Powertrain Control Module = Fuel Injection Computer) whether it's injecting to much fuel or not enough.

Once the engine is running and fuel is being injected into the engine, the PCM needs to constantly fine-tune the amount of injection. All this so that your car can get the maximum amount of miles per gallon of fuel consumed and to keep pollution down.

Here are some more specifics:

  1. 1

    As the engine runs, the PCM is constantly injecting fuel. If it injects too much, the oxygen sensor reacts by producing a voltage above 0.500 Volts (this voltage can go as high as 0.900 to 1.0 volt).

    Any voltage above 0.500 Volts, is considered a rich condition and when the PCM sees this rich condition, it starts to inject less fuel.

  2. 2

    As the PCM starts to inject less fuel, it may go too far and not inject enough. When the PCM does not inject enough fuel, this is known as a lean condition.

    This lean condition will make the O2 sensor produce and report a voltage below 0.500 Volts. Depending on how lean the air/fuel mixture is, the O2 sensor's voltage can go as low as 0.050 to 0.100 Volts.

    When the PCM sees these voltage numbers, it knows to inject more fuel.

  3. 3

    This process (of adjusting the amount of fuel being injected) by the PCM, goes on the entire time the engine is running (and if the O2 sensor is working correctly).

  4. 4

    All of these oxygen sensor voltages changes can be easily observed with a scan tool in Live Data mode, and this is how I'm gonna' show you how to test them.

  5. 5

    A correctly working O2 sensor will produce a voltage that will switch between a lean and rich condition several times every few seconds. So, if the voltage output of the O2 sensor stays fixed (when testing it), the O2 sensor has failed.

To find out what are some of the most common symptoms of a failed oxygen sensor, take a look at the section: Symptoms Of A Bad Oxygen Sensor.

More 1.6L Honda Civic Tutorials

I've written quite a few 1.6L ‘how to’ tutorials that may help you troubleshoot the issues on your Honda vehicle. You can find the complete list at:

Here's a sample of the Honda 1.6L articles you'll find:

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