# Clean O2 Sensor?



## PanJet (Jun 18, 2013)

Has anyone out of warranty who has P0133 code attempted to clean their own sensor rather than replacing it?

I ask because I have had P0133 pop up twice. The first was at about 25,000 miles. The dealer applied the fuel trim update and cleared the code. Then again about 500 miles later the code reappeared. I was expecting to have to replace the sensor, but instead the dealer told me they cleaned the sensor and reinstalled it. They told me if it happens again we'll reevaluate, and they are aware of the common problem with P0133.

It's been nearly 5,000 miles since they did that with no CEL.

How easy would it be to simply pull the sensor, clean it, and put it back in? Annoying, yes, but at least if the car is out of warranty I'm not having to pay for and wait for a new sensor.


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## diesel (Jun 8, 2013)

I haven't done it, but I would imagine it's reasonably easy to do.


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## oilburner (Jun 13, 2013)

easy , easy comes out like a spark plug. you will need a proper socket that has an open spot to slip over harness. clean the crap off it an reinstall.


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## PanJet (Jun 18, 2013)

So perhaps this is an effective method instead of replacement? How about cleaning method? Just brush it off? How sensitive is the sensor to damage?


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## PanJet (Jun 18, 2013)

Ugh, I spoke too soon. P0133 just came back on.  I'm still under warranty, so back to the dealer this week.


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## diesel (Jun 8, 2013)

PanJet said:


> Ugh, I spoke too soon. P0133 just came back on.  I'm still under warranty, so back to the dealer this week.


What did they use to clean it initially?


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## PanJet (Jun 18, 2013)

diesel said:


> What did they use to clean it initially?


He told me they just brushed it clean. I don't think they used any chemicals.


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## diesel (Jun 8, 2013)

MAF sensor cleaner comes to mind.


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## roadrunnerA12 (Jan 21, 2015)

A little too complicated to brush it off and put it back in. Nothing in the following suggests that there is an effective way to clean an O2 sensor. 
[h=5]How it Works[/h] The O2 sensor works like a miniature generator and produces its own voltage when it gets hot. Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb. The bulb is coated on the outside with a porous layer of platinum. Inside the bulb are two strips of platinum that serve as electrodes or contacts.
The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors "breathe" through their wire connectors and have no vent hole. It's hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail. The difference in oxygen levels between the exhaust and outside air within the sensor causes voltage to flow through the ceramic bulb. The greater the difference, the higher the voltage reading.
An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor's output voltage will drop down to about 0.1 volts. When the air/fuel mixture is balanced or at the equilibrium point of about 14.7 to 1, the sensor will read around 0.45 volts.
When the computer receives a rich signal (high voltage) from the O2 sensor, it leans the fuel mixture to reduce the sensor's reading. When the O2 sensor reading goes lean (low voltage), the computer reverses again making the fuel mixture go rich. This constant flip-flopping back and forth of the fuel mixture occurs with different speeds depending on the fuel system. The transition rate is slowest on engines with feedback carburetors, typically once per second at 2500 rpm. Engines with throttle body injection are somewhat faster (2 to 3 times per second at 2500 rpm), while engines with multiport injection are the fastest (5 to 7 times per second at 2500 rpm).
The oxygen sensor must be hot (about 600 degrees or higher) before it will start to generate a voltage signal, so many oxygen sensors have a small heating element inside to help them reach operating temperature more quickly. The heating element can also prevent the sensor from cooling off too much during prolonged idle, which would cause the system to revert to open loop.
Heated O2 sensors are used mostly in newer vehicles and typically have 3 or 4 wires. Older single wire O2 sensors do not have heaters. When replacing an O2 sensor, make sure it is the same type as the original (heated or unheated). 
[h=5]A New Role for O2 Sensors with OBDII[/h] Starting with a few vehicles in 1994 and 1995, and all 1996 and newer vehicles, the number of oxygen sensors per engine has doubled. A second oxygen sensor is now used downstream of the catalytic converter to monitor the converter's operating efficiency. On V6 or V8 engines with dual exhausts, this means up to four O2 sensors (one for each cylinder bank and one after each converter) may be used.
The OBDII system is designed to monitor the emissions performance of the engine. This includes keeping an eye on anything that might cause emissions to increase. The OBDII system compares the oxygen level readings of the O2 sensors before and after the converter to see if the converter is reducing the pollutants in the exhaust. If it sees little or no change in oxygen level readings, it means the converter is not working properly. This will cause the Malfunction Indicator Lamp (MIL) to come on. 
[h=5]Sensor Diagnosis[/h] O2 sensors are amazingly rugged considering the operating environment they live in. But O2 sensors do wear out and eventually have to be replaced. The performance of the O2 sensor tends to diminish with age as contaminants accumulate on the sensor tip and gradually reduce its ability to produce voltage. This kind of deterioration can be caused by a variety of substances that find their way into the exhaust such as lead, silicone, sulfur, oil ash and even some fuel additives. The sensor can also be damaged by environmental factors such as water, splash from road salt, oil and dirt.
As the sensor ages and becomes sluggish, the time it takes to react to changes in the air/fuel mixture slows down which causes emissions to go up. This happens because the flip-flopping of the fuel mixture is slowed down which reduces converter efficiency. The effect is more noticeable on engines with multiport fuel injection (MFI) than electronic carburetion or throttle body injection because the fuel ratio changes much more rapidly on MFI applications. If the sensor dies altogether, the result can be a fixed, rich fuel mixture. Default on most fuel injected applications is mid-range after three minutes. This causes a big jump in fuel consumption as well as emissions. And if the converter overheats because of the rich mixture, it may suffer damage. One EPA study found that 70% of the vehicles that failed an I/M 240 emissions test needed a new O2 sensor.
The only way to know if the O2 sensor is doing its job is to inspect it regularly. That's why some vehicles (mostly imports) have a sensor maintenance reminder light. A good time to check the sensor is when the spark plugs are changed.
You can read the O2 sensor's output with a scan tool or digital voltmeter, but the transitions are hard to see because the numbers jump around so much. Here's where a PC based scantool such as AutoTap really shines. You can use the graphing features to watch the transitions of the O2 sensors voltage. The software will display the sensor's voltage output as a wavy line that shows both it's amplitude (minimum and maximum voltage) as well as its frequency (transition rate from rich to lean). 
A good O2 sensor should produce an oscillating waveform at idle that makes voltage transitions from near minimum (0.1 v) to near maximum (0.9v). Making the fuel mixture artificially rich by feeding propane into the intake manifold should cause the sensor to respond almost immediately (within 100 milliseconds) and go to maximum (0.9v) output. Creating a lean mixture by opening a vacuum line should cause the sensor's output to drop to its minimum (0.1v) value. If the sensor doesn't flip-flop back and forth quickly enough, it may indicate a need for replacement.
If the O2 sensor circuit opens, shorts or goes out of range, it may set a fault code and illuminate the Check Engine or Malfunction Indicator Lamp. If additional diagnosis reveals the sensor is defective, replacement is required. But many O2 sensors that are badly degraded continue to work well enough not to set a fault code-but not well enough to prevent an increase in emissions and fuel consumption. The absence of a fault code or warning lamp, therefore, does not mean the O2 sensor is functioning properly.
[h=5]Sensor Replacement[/h] Any O2 sensor that is defective obviously needs to be replaced. But there may also be benefits to replacing the O2 sensor periodically for preventive maintenance. Replacing an aging O2 sensor that has become sluggish can restore peak fuel efficiency, minimize exhaust emissions and prolong the life of the converter.
Unheated 1 or 2 wire wire O2 sensors on 1976 through early 1990s vehicles can be replaced every 30,000 to 50,000 miles. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications can be changed every 60,000 miles. On OBDII equipped vehicles (1996 & up), a replacement interval of 100,000 miles is recommended.


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## KpaxFAQ (Sep 1, 2013)

When in doubt I get out MEK or brake cleaner


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## LulzT1 (Aug 24, 2015)

There's really no way to clean an O2 sensor. You're not going to accomplish much cleaning the protective steel cap unless it's so caked in soot the holes are covered, but if that's the case you have other issues. Using harsh chemicals on a sensor that measures between 0-1V doesn't sound like a good idea considering it affects how the ECM adjusts fueling and what not. Also, the sensor is exposed to some high temps, so anything on it is probably baked on pretty good. Since you're going back, question them why/how they cleaned it and see what they say. I'd also make them swap it out too.


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## obnxous (Jan 17, 2018)

Sorry I'm a little late to the party.
I've been researching how to properly clean the Oxygen sensors on a diesel car specifically without causing damage to the sensor (so far ive only found gas O2 sensor cleaning articles) when I found this post and article.

I have issues with the article.
The article says, "The O2 sensor works like a miniature generator and produces its own voltage when it gets hot"
ok, so since it produces voltage when it gets hot one would think that the hotter the sensor, the higher the voltage. From what we know about rich and lean conditions, a lean condition will burn hot (i.e. ref melted pistons, valves, spark plug electrodes etc exiting headers on NHRA dragsters on the far side of the track, also on your car if you're too lean for an extended period of time), and a rich condition burns cold (ref black carbon buildup on all internal engine and exhaust parts). However, the article references "An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich", and "When the mixture is lean, the sensor's output voltage will drop down to about 0.1 volts." 
This seems backwards to me. The hotter reading should produce the 0.9Volts where the cold reading, or rich read, would be the 0.1Volts.
Note: if the burn is hot, like during a regen, it will turn the carbon buildup to ash and clean parts. Supporting that logic, a rich condition will cause carbon buildup where a lean condition will burn the carbon buildup off and melt parts. When it comes to emissions, a rich condition will produce more CO, or carbon monoxide, where a lean condition will produce more NOx, or Nitrogen Oxide. (ref VW Dieselgate & https://www3.epa.gov/region1/airquality/nox.html)
Has anyone else noticed this discrepancy or am I all messed up?

Another thing the article does not mention is under 2000 RPMs, most computers only use the MAF or MAP sensors to determine mixture, based on air flow or absolute pressure. The computer typically doesn't even reference the Oxygen sensors until after 2000 RPMs. Otherwise, even though the oxygen sensor is reading the exhaust, the computer disregards the reading unless the car is moving.
I think I'm going to use Seafoam and a toothbrush to clean my sensor. I know Seafoam breaks down buildup, keeps the metal clean and doesn't leave any residue. I feel it may be the safest way to clean these sensors.


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## MRO1791 (Sep 2, 2016)

obnxous said:


> Sorry I'm a little late to the party.
> I've been researching how to properly clean the Oxygen sensors on a diesel car specifically without causing damage to the sensor (so far ive only found gas O2 sensor cleaning articles) when I found this post and article.
> 
> I have issues with the article.
> ...


I used compressed air, which will remove most of the soot (it should be dry soot on there, if something else you could have other problems). This is before the DPF, in the DPF canister. While you have the sensor out, you can blow in some compressed air in the hole and see the soot/carbon dust spray out of that hole.. You can also see where the DPF filter media starts, using a flashlight. 

I used some carburetor cleaner, and brake parts cleaner in addition to compressed air, but likely it would have been OK with just air. It should clean up pretty easy, the soot/carbon cakes up and blocks the sensor port, thus slowing the sensor response and hello P0133. I did see a noticeable improvement in MPG after I cleaned the sensor, and the twice prior P0133 code did not return, so I still have a spare O2 sensor if I ever need it (you can find them on Amazon, if you think you need one).


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