Every vehicle built since the early 1980’s has one or more (O2) oxygen sensors integrated into the exhaust system.
(O2) oxygen sensors are used to confirm that the proper air fuel ratio is actually reaching the engine.
Measuring the (O2) oxygen level in the exhaust provides a good gauge of what the fuel to oxygen ratio is. Consequently, Its job is to measure the amount of unburnt (O2) oxygen exiting the engine.
Also, (O2) oxygen sensors are a very important part of your vehicle’s emission system. The emission system is designed to reduce the amount of dangerous gasses discharged into the environment.
The level of (O2) oxygen in the exhaust is measured and sent to the engine control unit (ECU) for analysis.
If the fuel mixture has too much oxygen, the engine is burning lean. If the fuel mixture has too little oxygen, the engine is burning rich.
In either case, the (ECU) needs this information in order to adjust the fuel/oxygen ratio. Finally, if your vehicle has a defective (O2) sensor, it will not run efficiently.
Symptoms Of Bad Or Failing (O2) Oxygen Sensors
The (O2) oxygen sensor is not easy to get to or observe because of its physical location. For that reason, there are several warning signs that will alert you that there may be a problem.
Several of the most obvious warning signs that the (O2) oxygen sensor is failing include:
- Reduced gas mileage
- A bad smell like rotten eggs coming from the exhaust
- The check engine light comes on
- You notice that your engine idles roughly
- The vehicle is suddenly hard to start
Check Engine Light (CIL)
Usually, a check engine light will provide the first indication that you might have a bad (O2) oxygen sensor.
Often, the engine code will simply state that there is a problem with the (O2) oxygen sensor. Sometimes, it may say that there is a “heater circuit malfunction.”
(O2) oxygen sensors can be very expensive to replace. However, the problem might not be with the (O2) oxygen sensor at all. Because, other factors may be involved, it is a good idea to test your (O2) oxygen sensor before replacing it.
Testing Procedures (O2) Oxygen Sensors
Oxygen sensors can be tested both on or off the vehicle. However, by taking the oxygen sensor off, you are able to visually inspect the sensor.
As a result, often provide a good indication that there is a problem. Furthermore, making the sensor a little easier to test.
Using A Digital Voltmeter
Above all, the results of this test may require further analysis of other components:
- Maybe there is a loose vacuum hose that is forcing the (O2) sensor to read a high level of oxygen.
- Maybe a loose connection to the (O2) oxygen sensor is causing it to incorrectly read the exhaust gasses.
- You just don’t know until you measure the (O2) oxygen sensors operating characteristics.
Let’s look at diagnosing the problem by measuring the (O2) oxygen sensors operating characteristics:
Identify the specific (O2) oxygen sensor that you want to do the test on. Depending on the year of your vehicle there could be up to 5 (O2) oxygen sensors in the exhaust system. Fortunately, the computer (DTC) will pinpoint the specific (O2) oxygen sensor that needs to be tested.
Using the (DTC), you can refer to your owner’s manual to locate the sensor. Your owner’s manual will also identify the signal wire as many (O2) oxygen sensors have multiple wires connected to them.
You will need a 10-megaohm impedance digital voltmeter for testing the (O2) oxygen sensor.
You should set it to the millivolt (mV) DC scale.
Now start the vehicle and let it run until it reaches operating temperature. This may take up to 20 minutes:
- Once you have reached operating temperature, turn off the engine.
- Now connect the red probe to the (O2) oxygen sensors signal wire and the black probe to a good ground.
- To perform the actual test, start the engine again and check the voltage readings.
- The (O2) oxygen sensors voltage should fluctuate within the 100mV – 900mV (0.10V to 0.90V) range.
- If it is within this range, the (O2) oxygen sensor is operating normally and you can stop testing.
In case it is not within range, there is either an engine problem or the (O2) oxygen sensor is bad. If it appears to be bad, continue with the next steps.
Test the (O2) oxygen sensor response to a lean fuel consumption situation:
- Disconnect the hose from the positive crankcase ventilation (PVC) valve which is located on the valve cover.
- This will allow more air into the engine so the voltmeter should read close to 200mV (0.20V).
If the voltmeter does not respond, the (O2) oxygen sensor is not functioning properly.
Reconnect the (PVC) hose to test the (O2) oxygen sensors response to a rich fuel consumption situation:
- To do this disconnect the plastic hose connection to the air cleaner assembly.
- Block the hose connection opening with a rag in order to reduce the amount of air going into the engine.
- Check the voltmeter. It should read close to 800mV (0.08V) due to the reduction of oxygen entering the engine.
If the (O2) oxygen sensor does not respond this way, it is not functioning properly.
Reconnect the hose to the air cleaner:
- If the (O2) oxygen sensor responded correctly to the lean and rich fuel tests; another component could be causing the problem.
- The potential issues could be a vacuum leak, ignition system or something similar.
Obviously, if the (O2) oxygen sensor did not respond properly then it is bad and will need to be replaced.
So, after all your testing you should know whether the (O2) oxygen sensor is bad; or if something else is the problem. If you feel confident that the (O2) oxygen sensor is bad, just replace it.
So, remember, addressing the problem sooner than later may save you from more serious issues. Obviously, the logical choice is to replace the failed (O2) oxygen sensor yourself. Finally, saving a bunch of money on costly repairs.
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