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

Oxygen Sensor Basics

As mentioned before, your 1.5L Honda Civic's fuel injection computer uses the oxygen sensor as a feedback sensor to find out whether it's injecting to much fuel or not enough.

You and I can find out if the oxygen sensor is doing its job by tapping into its signal wire with a multimeter. But to really understand how the O2 sensor reports a rich or a lean condition we need to know how it works.

Here are some more specifics:

  1. 1

    As the engine runs, the computer 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, and the fuel injection computer considers this a Rich condition. When the computer sees this Rich condition, it starts to inject less fuel.

  2. 2

    As the computer starts to inject less fuel it may go too far and not inject enough. When the computer does not inject enough fuel the O2 sensor reacts by producing 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 computer sees these voltage numbers, it knows it's creating a Lean air/fuel mixture and starts to inject more fuel.

  3. 3

    This process of adjusting the amount of fuel being injected to compensate for the alternating rich and lean conditions caused by the computer 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 multimeter in Volts DC 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.

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.

More 1.5L Honda Test Tutorials

I've written quite a few 1.5L Honda Civic tutorials that may help you troubleshoot the issues on your Honda Civic. You can find the complete list at: Honda 1.5L Index Of Articles.

Here's a sample of the Honda 1.5L articles you'll find:

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Honda Vehicles:

  • Civic CX 1.5L
    • 1992, 1993, 1994
  • Civic 1.5L
    • 1991
  • Civic CRX 1.5L
    • 1991