Oxygen (O2) sensors are critical to the proper calculation of the air-fuel mixture that runs through the engine. But like other components, they can fail after some time, leading to several performance problems.
Some drivers try to save a couple of bucks by resorting to DIY cleaning methods instead of simply buying a replacement sensor.
Note: For an in-depth background on oxygen sensors, read our discussion about air-fuel mixtures. If it’s your first time locating your vehicle’s oxygen sensors, be sure to learn about the difference between bank 1 and bank 2, as well as rich and lean diagnostic codes.
Can You Clean an O2 Sensor?
A dirty or faulty oxygen sensor is meant to be replaced, not cleaned.
The caveat is that if the O2 sensor is simply coated with soot from a temporary rich condition, repairing the rich condition will typically enable the lean, clean exhaust to burn the soot off. However, O2 sensors can become sluggish over time. Since the early 2000s, O2 sensors have become much more reliable.
One thing that will ruin an O2 sensor is a coolant leak into the exhaust, particularly if the coolant has silicone as a part of its formula. Silicone will coat a zirconia sensor and render it inoperative.
The caveat is that if the O2 sensor is simply coated with soot from a temporary rich condition, repairing the rich condition will typically enable the lean, clean exhaust to burn the soot off. However, O2 sensors can become sluggish over time. Since the early 2000s, O2 sensors have become much more reliable.
– Richard McCuistian, ASE Certified Master Automobile Technician
Most car manufacturers don’t recommend cleaning an O2 sensor with a wire brush or aerosol cleaner. Cleaning the sensor this way is ineffective because you can’t physically get to the zirconia bulb part of the sensor that creates the voltage. If the zirconia bulb is coated with material, trying to remove the sensor and clean it just won’t work.
Cleaning with a wire brush or aerosol cleaner can increase the risk of damaging the sensor and altering the air-fuel mixture. Plus, removing the sensor multiple times can damage the threads. More importantly, you risk voiding a warranty if you try to clean the O2 sensor by yourself and something goes wrong with your vehicle later.
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Pro Tip: If you do have to remove the sensor, make sure you put anti-seize compound on the threads to prevent the threads from galling, because they will. New O2 sensors come with anti-seize compound on the threads. Note that if the last person who removed the sensor put it back without anti-seize, you may have to use an 18mm spark plug tap to chase the threads in the exhaust.
How Does an O2 Sensor Work?
The O2 sensor is in the exhaust manifold or downstream from the manifold in the exhaust pipe. It’s directly in the path of the exhaust gas stream where it monitors the O2 levels in the exhaust stream and ambient air.
The powertrain control module (PCM) uses the O2 sensor for fuel control and fuel trim.
Fuel Control
The PCM receives initial input from the engine coolant temperature (ECT) sensor, throttle position (TP) sensor, and other related components for proper fuel delivery.
Once the O2 sensor has all the information to supply rich and lean signals to the PCM, the computer will be able to fine-tune the correct air-fuel mixture.
The upstream oxygen sensor usually has the information for proper fuel control while operating in a closed loop, which is the PCM’s activity of checking and adjusting the mixture.
Fuel Trim
The O2 sensor is responsible for supplying the fuel trim numbers.
The PCM uses these fuel trim numbers to make the necessary adjustments when air-fuel ratio problems are detected.
You can also check this video to get an idea of how oxygen sensors work:
Symptoms of a Faulty O2 Sensor
A faulty O2 sensor can cause your vehicle to exhibit the following symptoms.
Illuminated Check Engine Light
Oxygen sensors help diagnose other systems and components. Once they fail, the powertrain control module won’t be able to monitor other systems. A bad O2 sensor will cause the PCM to trigger the check engine light and store a diagnostic trouble code (DTC).
Engine Performance Issues
Misfiring, rough running, and stalling are common signs that point to a faulty oxygen sensor. This is because the sensor is unable to calculate the right air-fuel mixture.
Poor Fuel Economy
A faulty O2 sensor can produce an overly rich air-fuel mixture, causing the vehicle to consume more fuel than necessary. It can also cause the catalytic converter to overheat and fail after some time.
What to Expect When Replacing a Faulty O2 Sensor
The condition of the old O2 sensor can help you determine the cause of failure. Here are some things you might see while inspecting the sensor.
Black Sooty Deposits
Black sooty deposits usually indicate a rich air-fuel mixture. This means that an excessive proportion of fuel is present because less air in the mixture can lead to incomplete fuel combustion.
White Chalky Deposits
These deposits are indicative of silica contamination. Using the wrong type of silicone sealant when servicing the engine and silica deposits in the fuel can cause this problem.
White Sandy or Gritty Deposits
These kinds of deposits indicate antifreeze (ethylene glycol) contamination and might also cause the O2 sensor to turn green because of the antifreeze dye.
A defective cylinder head, intake manifold gasket, cylinder head, or cracked engine block can cause white, sandy, or gritty deposits.
Dark Brown Deposits
Dark brown deposits could mean that the engine is consuming too much oil.
A defective positive crankcase ventilation (PCV) system or a mechanical engine problem like defective valve stem seals or piston rings can cause these buildups.
Check out these videos about replacing your oxygen sensors:
Can You Drive with a Bad Oxygen Sensor?
You can drive for a few miles with a bad oxygen sensor, but experts don’t recommend doing it.
Driving with a bad oxygen sensor can clog the catalytic converter because of excessive fuel. As a result, you’ll be paying an additional fee to get the catalytic converter fixed instead of simply replacing the damaged O2 sensor.
How Many O2 Sensors Does a Vehicle Have?
The number of O2 sensors in a vehicle depends on its year, make, and model.
Most four and six-cylinder engines have one O2 sensor mounted in the exhaust manifold. Meanwhile, most V6, V8, and V10 engines have two O2 sensors in each exhaust manifold.
Some late-model vehicles with on-board diagnostics (OBD-II) have one or two additional sensors inside or behind the catalytic converter. These are referred to as downstream O2 sensors.
O2 Sensor Designs
There are generally four O2 sensor designs: one-wire, two-wire, three-wire, and four-wire.
One-Wire O2 Sensor
A one-wire O2 sensor has a lone signal wire. Its ground goes into the sensor’s shell and threads and passes through the exhaust manifold.
Two-Wire O2 Sensor
This O2 sensor comes with a separate signal and ground wire.
Three-Wire O2 Sensor
A three-wire O2 sensor comes with an electric resistance heater that helps the sensor reach its operating temperature more quickly. The three wires include the O2 sensor signal, power, and ground for the electric resistance heater.
Four-Wire O2 Sensor
A four-wire O2 sensor is a heated sensor that has a separate signal and ground wire. The remaining wires serve as the power and ground for the heater.
Get a New Oxygen Sensor Delivered to Your Home
Until you’ve replaced the malfunctioning oxygen sensor, it might be best to stop driving your vehicle. Engine repair jobs are usually costly, so you want to prevent issues with other parts. Get your car or truck back on the road with a new oxygen sensor from CarParts.com.
CarParts.com delivers the competitively priced, high-quality oxygen sensors you ordered to where you need them. We operate several distribution centers in strategic locations across the US, which helps reduce delivery times. The nearest center processes your order with the latest technologies before shipping your new part to your address. You don’t have to wait more than several business days for your replacement part to arrive if you live in the continental US and place your order before 12 p.m. ET. Furthermore, we guarantee the reliability and performance of our oxygen sensors by exclusively sourcing our parts from trusted manufacturers.
When it’s time to replace dirty or worn-out oxygen sensors, make CarParts.com your one-stop shop for replacement parts. Order one of our oxygen sensors today and enjoy fast delivery of your new parts!
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Another excellent article by Richard McCuistian – very informative and straight forward explanations.
The information about the causes for different colors of deposits was very interesting and helpful. I didn’t know that before. I would never try to clean an old O2 sensor. However, knowing the reason for a color of soot, is helpful for finding and fixing the root cause of the dirty sensor. Otherwise, a new replacement sensor will get the same sooty build-up.
The sensors for my car cost about $25 each (two required). After spending the time to remove and replace a sensor, why rick putting a faulty sensor back in (after attempting to clean it) and not knowing if it is sending erroneous information the the ECM/PCM.
Overall, it’s less work to not try to clean it, and just remove the old sensor and replace with a new one. Then you know the ECM/PCM will be correctly managing the fuel and the engine running at its best.
Trying to save some money on the new parts, will soon cost even more in wasted gas.
What is the old saying: “Penny Wise and Pound Foolish“?
Question to the author:
White Chalky Deposits
“These deposits are indicative of silica contamination. Using the wrong type of silicone sealant when servicing the engine and silica deposits in the fuel can cause this problem.”
How does silica get in the fuel?