TEST 2: Manually Creating A Rich Condition To Test The O2 Sensor
Manually inducing a rich air/fuel mixture condition is one of the best ways to test oxygen sensor performance.
We can easily induce a rich condition in the exhaust stream by spraying a little starting fluid (or carb cleaner spray) into the throttle body while the engine is running.
If the oxygen sensor is OK, it will immediately generate 0.900 Volts, which your multimeter will confirm.
If the sensor is faulty (or too slow, which is also bad), enriching the air/fuel mixture with carb spray will not raise the voltage to 0.9 Volts, or it will take forever for the voltage to increase.
NOTE: Your multimeter must remain connected to the O2 sensor wire as in the previous test.
Alright, this is what you'll need to do:
- 1
Remove the cover from the air cleaner assembly and start and let the engine run for about 15 minutes to get the O2 sensor to activate.
- 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
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. - 4
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.
- 5
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: 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.
Your next step is to check the oxygen sensor under a lean air-fuel mixture condition. For this test go to: TEST 3: Manually Creating A Lean Condition To Test The O2 Sensor.
CASE 2: 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
If your test results indicate that the oxygen sensor is stuck and reporting a continuous rich condition, chances are the O2 sensor is faulty or it's just reporting an actual engine performance problem.
By manually inducing a lean air/fuel condition, we can see if the oxygen sensor reacts to it or not.
If the O2 sensor does not respond to the induced lean condition, you can conclude that the sensor is bad and needs to be replaced.
If the O2 sensor responds to the lean condition, you can conclude that the O2 sensor is good and doing its job of reporting an engine performance problem.
NOTE: Your multimeter must remain connected to the O2 sensor wire as in the previous test.
OK, these are the test steps:
- 1
Start and let the engine run for about 15 minutes to get the O2 sensor to activate.
- 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
With the engine running, slightly disconnect the vacuum hose from the brake booster while you observe your multimeter's display screen.
If the engine stalls when you open the brake booster vacuum hose, restart the engine and open the brake booster vacuum hose less. - 4
You should see the O2 sensor voltage numbers immediately 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
Reconnecting the brake booster hose 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: O2 sensor voltage numbers drop to 0.200 Volts or less when you slightly opened the brake booster vacuum hose. 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: O2 sensor voltage numbers DID NOT drop to 0.200 Volts or less when you slightly opened the brake booster vacuum hose. This confirms that oxygen sensor is no longer working. You can replace the oxygen sensor.
More 2.8L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials
You can find a complete list of tutorials for the 2.8L V6 Chevrolet S10 pickup, GMC S15 pickup, and GMC Sonoma in this index:
Here's a sample of the articles, you'll find in the Index of Articles:
- How To Test The Fuel Pump (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test Engine Compression (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test The EGR Valve (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test The Starter Motor (1988-1993 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup).
If this info saved the day, buy me a beer!
