How To Test The Upstream Oxygen Sensor (Honda 2.2L, 2.3L)

By: Abraham Torres-Arredondo
Created: 21 July 2011
Updated: 06 September 2025
Articl Id: 254

You can test the upstream oxygen sensor (commonly known as the O2 Sensor Bank 1 Sensor 1: O2S11) before replacing it to make sure it's really bad, and in this article, I'll show you how.

The most common symptom of a failed O2 sensor is the OBD II codes P0131, P0133. What sucks is that the PCM may think they're bad when they're really not. S testing them makes a lot of sense.

Contents of this tutorial:

Important Suggestions And Tips.
Symptoms Of A Bad Oxygen Sensor.
Oxygen Sensor Basics.
O2 SENSOR TEST: Manually Inducing A Rich Condition.
Oxygen Sensor Codes Keep Coming Back.
More Test Articles.

APPLIES TO: This tutorial applies to the following vehicles:

2.2L Honda Accord: 1996, 1997.
2.3L Honda Accord: 1998, 1999, 2000, 2001, 2002.

Important Suggestions And Tips

TIP 1: A scan tool with Live Data capability is a must to use the testing info in this article.

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. If you don't have a scan tool and need to buy one, check out my recommendation here: ZM301 OBD2 Scanner Diagnostic Tool (Amazon affiliate link).

TIP 2: The oxygen sensor test, I'm gonna' show you in this article, is an on-car test, so you do not need to remove it to test it.

Symptoms Of A Bad Oxygen Sensor

The effects of a bad oxygen sensor can be very subtle since they usually do not cause serious drive-ability problems.

For the most part, you're able to drive your Honda normally. As if nothing were wrong (although not in all cases).

Here are the most common symptoms:

The check engine light (CEL) will be illuminated on your instrument cluster.
The diagnostic trouble codes lighting up the CEL usually are:
- 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 (smog check).

Oxygen Sensor Basics

The oxygen sensor is tasked with helping the PCM (Powertrain Control Module = Fuel Injection Computer) fine-tune the amount of fuel that's being injected into the cylinders.

This fine-tuning helps control emissions and improves gas mileage. How? By reporting if the air/fuel mixture is either rich or lean.

Rich means the PCM is injecting too much fuel for the amount of available air entering the cylinder, and lean means not enough fuel is being injected.

Here are some more specifics:

As the engine runs, the PCM is constantly injecting fuel.
If it injects too much, the air/fuel mixture will run rich, and the oxygen sensor reacts by producing a voltage above 0.500 Volts.
- Depending on how rich the air/fuel mixture is, this voltage can go as high as 0.900 to 1.0 Volt.
As soon as the PCM sees the air/fuel mixture going rich, it starts to inject less fuel.
As the PCM injects less fuel, it may go too far and not inject enough. The resulting 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.
This process of adjusting the amount of fuel being injected goes on the entire time the engine is running (if the O2 sensor is working correctly).
- A correctly working O2 sensor will produce a voltage that switches between a lean and rich condition several times every few seconds.

All of these oxygen sensor voltage 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.

O2 SENSOR TEST: Manually Inducing A Rich Condition

Manually Inducing A Rich Condition. How To Test The Upstream Oxygen Sensor (Honda 2.2L, 2.3L)

To test the oxygen sensor (O2S11), we're going to manually induce a rich condition and see how the sensor reacts.

This can be done by spraying a little carburetor cleaner into the engine while it's running. My preferred method is to spray carb spray into a vacuum hose.

You can also open up the top portion of the air filter box and spray into it (it'll get sucked into the engine since the air intake duct connects to it), or disconnect the air intake duct at the throttle body and spray directly into the throttle body bore.

Once the carb spray hits the engine cylinders, you'll get an instant rich condition. This will make the O2 sensor respond by producing its maximum voltage (0.900 Volts +), and you'll be able to see this on your scan tool (in Live Data mode).

Alright, this is what you'll need to do:

1
Start your vehicle and let it idle for about 15 minutes.

NOTE: It's important for the engine to reach its normal operating temp to get the O2 sensor to activate and to get an accurate reading.
2
Connect your scan tool and go to its live data mode.
3
Once you're in live data mode, scroll down to the PID labeled O2S11.

This parameter ID will show you the front oxygen sensor voltage activity.
4
You should see the voltage numbers of the O2 sensor moving between 0.100 and 0.900 Volts constantly.

If the voltage value stays fixed, don't worry about it yet —continue to the next step.
5
With the engine running, spray a little carburetor cleaner into the throttle body while you observe your scan tool's display screen.

If you spray too much, the engine will stall. If this happens, just restart the engine, repeat the step, and spray less carb cleaner.
6
As you spray some short bursts of carb cleaner, you should see the voltage numbers of O2S11 immediately spike to 0.800 to 0.900 Volts.
7
When you stop spraying, the O2 sensor values should come down, and within a few seconds, they should start oscillating between 0.100 and 0.900 Volts.

OK, the test is done. Let's take a look at what your test results mean:

CASE 1: O2S11 voltage numbers spiked to 0.900 Volts when you sprayed carb spray into the vacuum hose. This tells you that the oxygen sensor is OK at this point in time.

It does not need to be replaced, since whatever's causing the PCM to think it's fried is something else.

For more info on this, go to the section: Oxygen Sensor Codes Keep Coming Back.

CASE 2: O2S11 voltage numbers DID NOT spike to 0.900 Volts when you sprayed carb spray into the vacuum hose. This confirms that the front oxygen sensor is no longer working. You can replace the oxygen sensor.

Oxygen Sensor Codes Keep Coming Back

So you tested the oxygen sensor and they tested good or you have already replace one or both and yet the PCM keeps accusing them as being bad (which also means that the check engine light is back on).

When this happens, it's usually due to either a rich condition or lean condition that's being caused by some other component on the engine.

What sucks about this, is that whatever is causing the rich or lean condition is not present all of the time (specially when you're conducting the tests). This happens quite a bit. The strategy here is to wait a few days for the condition (that's causing the O2 sensor issues) to get worse. When this occurs, you'll be able to test it and solve it.