How To Test The Front Oxygen Sensor With A Multimeter (2.2L GM)

TEST 2: Manually Creating A Rich Condition To Test The O2 Sensor

In this test section, we're gonna' alter the air/fuel mixture the engine is burning to see if the O2 sensor reports it.

We'll start off by inducing a rich condition, manually of course, by spraying a little starting fluid (or carburetor cleaner) into the throttle body while the engine is running.

If the oxygen sensor is good, it'll immediately produce 0.900 Volts and you'll be able to see this on your multimeter's display.

If the sensor is bad (or too slow, which also equals bad), then forcing a rich air/fuel mixture (with carb spray) won't increase its signal voltage to 0.9 Volts or it'll take forever to increase.

NOTE: Your multimeter must remain connected to the O2 sensor wire as from the previous test.

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

1. 1

   Crank and start the engine. Let it run for about 15 minutes to get the O2 sensor to activate.
   
   Once the engine has warmed up, turn it off and remove the air duct connected to the throttle body.

2. 2

   Restart the engine and let it run for one minute at 2000 RPMs (to get the O2 sensor to activate once again).

3. 3

   Let the engine return to idle (after the minute is over) and observe your multimeter's O2 sensor voltage readings. IF the 02 sensor is OK, you should see the voltages moving between 0.200 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, continue on to the next step.

4. 4

   With the engine running, spray a little starting fluid (or carburetor cleaner) into throttle body while you observe your multimeter's display screen.
   
   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.

5. 5

   As you spray some short burst of starting fluid or carb cleaner into the throttle body, you should see the O2 sensor voltage numbers immediately spike to 0.800 to 0.900 Volts. And as long as you're spraying, these voltage number should stay there.

6. 6

   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.

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

CASE 1: The O2 sensor voltage numbers spiked to 0.900 Volts when you sprayed carb spray into the throttle body. 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.

CASE 2: The O2 sensor voltage numbers DID NOT spike to 0.900 Volts when you sprayed starting fluid (or carb spray) into the throttle body. This confirms that oxygen sensor is no longer working. You can replace the oxygen sensor.

TEST 3: Manually Creating A Lean Condition To Test The O2 Sensor

In this test section, we're going to force the air/fuel mixture to go lean. This will help see if the O2 sensor can sense this Lean condition (the O2 sensor should report around 0.2 Volts DC if it senses our forced lean condition).

Forcing a lean condition, for the O2 sensor to sense, is helpful when your test results indicate the oxygen sensor is stuck reporting a continuous rich condition.

If when we induce a manual lean air/fuel mixture condition and the sensor does not react to it, then you can conclude it's bad and needs to be replaced.

If the O2 sensor does respond to the lean condition, then you can conclude the O2 sensor is fine and doing its job of reporting an engine performance issue.

NOTE: Your multimeter must remain connected to the O2 sensor wire as from the previous test.

OK, these are the test steps:

1. 1

   Start and let the engine run for about 15 minutes to get the O2 sensor to activate.

2. 2

   Observe your multimeter's O2 sensor voltage readings. IF the 02 sensor is OK, you should see the voltages moving between 0.200 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, continue on to the next step.

3. 3

   With the engine running, remove the PCV valve from the valve cover while you observe your multimeter's display screen.

4. 4

   You should see the O2 sensor voltage numbers mediately drop to 0.1 to 0.2 Volts. This drop will be momentary because the PCM will start to compensate by injecting more fuel.

5. 5

   Connecting the PCV valve should stop the voltage drop and within a few seconds, they should start oscillating between 0.100 Volts to 0.900 Volts.

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

CASE 1: The O2 sensor voltage numbers drop to 0.200 Volts or less when you removed the PCV valve from the valve cover. This tells you that the oxygen sensor is OK at this point in time. It does tell you that there's a problem causing a rich condition.

CASE 2: The O2 sensor voltage numbers DID NOT drop to 0.200 Volts or less when you disconnected the PCV valve. This confirms that oxygen sensor is no longer working. You can replace the oxygen sensor.

More 2.2L GM Diagnostic Tutorials

You can find a complete list of 2.2L GM tutorials in the following 2 indexes:

• GM 2.2L Index Of Articles.
• GM 2.2L Index Of Articles (at troubleshootmyvehicle.com).

Here's a small sample of the tutorials you'll find in the indexes:

• Oxygen Sensor Heater Test -P0141 (1995-1998 2.2L Cavalier / Sunfire).
• How To Test The GM 2.2L Throttle Position Sensor (TPS).
• How To Test The GM 2.2L Ignition Coil Pack.
• How To Test The Fuel Injectors With a Multimeter (GM 2.2L) (at: troubleshootmyvehicle.com).