Start Your Troubleshooting Here
The way this tutorial is set up, you'll be able to troubleshoot the upstream oxygen sensor in more than one way. I'll explain: You can do a simple oxygen sensor performance check or you can diagnose one of the following diagnostic trouble codes: P0131, P0132, or P0133.
Each specific test page will offer you specific testing info that's particular to that trouble code. To make it easier for you to find the right testing info, you can follow these links (all of these will take you to a specific page in this tutorial):
- Basic Upstream Oxygen Sensor Performance Test.
- P0131 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1).
- P0132 O2 Sensor Circuit Slow Response (Bank 1 Sensor 1).
- P0133 O2 Sensor Circuit Out Of Range Low Voltage (Bank 1 Sensor 1).
Basic Upstream Oxygen Sensor Performance Test
If you suspect that the O2 sensor has failed on your 3.8L equipped GM car or mini-van but aren't quite sure (because you have no trouble codes), then this test section is for you.
In a nutshell, to see if the O2 sensor (O2S11) has failed in your car or mini-van, you'll create a Rich condition and then see if the O2 sensor produces the correct report (on your scan tool).
To do this, you'll need to spray a little carburetor cleaner into an available vacuum hose while the engine is running.
If the oxygen sensor (O2S11) is good, it'll report a voltage between 0.800 to 0.900 Volts when the carb spray hits the cylinders and gets burned.
Alright, this is what you'll need to do:
Connect your scan tool to the your car or mini-van and start the engine (Don't have a scan tool? Need a scan tool? check out my recommendation: Actron CP9580 Scan Tool Review).
Let the engine idle for at least 15 minutes before you start the test, to get the O2 sensor to activate.
Now, on your scan tool (and once you're in Live Data mode), scroll down to the PID that's labeled O2S11. This PID is the one that will show you what the oxygen sensor is reporting in Volts DC.
Now, take a look at the voltage readings for O2S11.
These should be constantly moving between any number between 0.100 Volts and 0.900 Volts.
If the voltages are not moving between 0.100 and 0.900 Volts, don't worry about it just yet, let's go on to the next step.
With the engine running, spray a little carburetor cleaner into a vacuum hose (that has engine vacuum) while you observe your scan tool's display screen.
You're not going to be able to spray carb cleaner into the throttle as the engine is running, because if you were to do this, the engine will die as soon as you disconnect the air duct from it (to spray into it).
If you spray too much, the engine will stall. If this happens to you, just restart the engine and repeat the step and spray less carb cleaner spray.
As you spray some short burst of carb cleaner into the vacuum hose, you should see the voltage numbers of O2S11 immediately spike to 0.800 to 0.900 Volts. And as long as you're spraying, these voltage number should stay there.
When you stop spraying, the O2 sensor values should come down and within a few seconds, they should start oscillating between 0.100 Volts to 0.900 Volts. If they don't, don't worry about it yet.
OK, the test is done, let's take a look at what your test results mean:
CASE 1: The upstream O2 sensor's 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.
CASE 2: The upstream O2 sensor's voltage numbers DID NOT spike to 0.900 Volts when you sprayed carb spray into the vacuum hose. This confirms that Bank 1 Oxygen Sensor 1 is no longer working. You can replace the oxygen sensor.
To explain this a bit further, the front oxygen sensor should respond to the carb spray immediately by producing a voltage around 0.9 to 1 Volt DC. Since it didn't do this, you can safely assume the front oxygen sensor is either too worn out to respond or it's defective.