This article will help you to test the upstream oxygen sensor on your 2.4L Nissan Altima, Xterra or Frontier and/or troubleshoot OBD II Codes P0131, P0133.
The upstream oxygen sensor is the one before the catalytic converter and is also known as O2S11.
Contents of this tutorial:
Important Suggestions And Tips
TIP 1: You will need a scan tool to use the testing info in this article. Your scan tool must have Live Data capability since a simple code reader won't help you.
You don't need the Nissan 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 (Don't have a scan tool? Need a scan tool? Check out my recommendation: Actron CP9580 Scan Tool Review).
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.
Oxygen Sensor Basics
The job of the O2 Sensor, in your 2.4L Nissan Altima (Frontier, Xterra), is to help the PCM (Powertrain Control Module = Fuel Injection Computer) fine tune the amount of fuel that it injects into the engine.
If the PCM injects too much fuel, this is referred to as a Rich Condition. If it doesn't inject enough, the resulting Air/Fuel Mixture is said to be Lean. And so, it's the job of the O2 Sensor to measure just how Rich or Lean the exhaust is and report it back to the PCM.
Here are some more specifics:
If, after the engine is running and the PCM creates a Rich Condition, the oxygen sensor will react by producing a voltage above 0.500 Volts. Depending on how Rich the Air/Fuel Mixture, this voltage can go as high as 0.900 to 1.0 Volt.
As soon as the PCM sees this, it starts to inject less fuel.
As the PCM starts to inject less fuel.. it may go too far and not inject enough. This will cause a Lean Condition that will make the O2 sensor produce 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) by the PCM, goes on the entire time the engine is running (and if the O2 sensor is working correctly).
All of these oxygen sensor voltages changes can be easily observed with a scan tool in Live Date mode, and this is how I'm gonna' show you how to test them.
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. OK, let's turn the page and let's get testing...
O2 SENSOR TEST 1: Inducing a Rich Condition
To test the oxygen sensor (O2S11), the very first thing you'll do is to induce a Rich Condition.
This can easily 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.
Once the carb spray hits the engine cylinders, you'll get an instant Rich Condition which 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:
Start you vehicle and let it idle for about 15 minutes, since you need a warmed up engine to get the O2 sensor to activate. (Don't have a scan tool? Need a scan tool? Check out my recommendation: Actron CP9580 Scan Tool Review).
Connect your scan tool and get to its Live Data mode.
Once you're in Live Data mode, scroll down to the PID that's labeled O2S11. This PID will show you the oxygen sensor voltage activity.
What you should see, if the engine has been idling for about 15 minutes, are 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 this yet... continue to the next step.
STEP 4 Continued in the next page...