Something i'd like to address with questions about o2 sensors

[pandorasboyfriend]

I see questions over and over again. You don't have to replace them. All you have to do is clean them. If you're mechically inclined to remove them, just get a needle from grandma's sewing kit and start scraping the inside of the sensor through the little bitty holes that you see at the tip of the sensor. Blow the carbon off with your lungs each time you scrap. Screw the O2 back on and it's a done deal. This goes for all cars. If you don't have a computer to earse the MIL or service engine light, then just disconnect the battey before you clean the O2 sensor and reconnect the battery after you've re-installed the O2. Wait a couple of seconds and light will come off.

This is of course if you don't have a bad catilytic converter, plus it's a dang good place to start if you do have a bad catilytic converter to find the problem with O2 codes.

[Joe 1320]

I see questions over and over again. You don't have to replace them. All you have to do is clean them. If you're mechically inclined to remove them, just get a needle from grandma's sewing kit and start scraping the inside of the sensor through the little bitty holes that you see at the tip of the sensor. Blow the carbon off with your lungs each time you scrap. Screw the O2 back on and it's a done deal. This goes for all cars. If you don't have a computer to earse the MIL or service engine light, then just disconnect the battey before you clean the O2 sensor and reconnect the battery after you've re-installed the O2. Wait a couple of seconds and light will come off.

This is of course if you don't have a bad catilytic converter, plus it's a dang good place to start if you do have a bad catilytic converter to find the problem with O2 codes.

It appears that you don't have a complete understanding of the construction and what happens to an Oxygen sensor as it degrades. The proceedure you describe will only work in limited circumstances, mostly when the engine has carbon build up from a poor state of tune.

The later oxygen sensors from the early 90s and later are heated sensors, using a seperate voltage line to bring the sensor up to operating temperature much sooner than the single wire non heated sensors. This is mainly to prevent carbon buildup and to decrease emissions. Often times the heating element quits, setting an SES light and subsequent code. The sensor may still work, albiet not very well until it reaches it's normal operating temperature. Cleaning will not help, replacement is the only option. Next is the issue of chemical or particle contamination. If you get a coolant leak into a combustion chamber or manage to get RTV in the exhaust from sloppy handling or using it as an exhaust gasket, expect the sensor to become contaminated and it's toast. Compound that with the fact that the switching rate declines as it ages so it becomes slower to respond, throttle response gradually declines and so does gas mileage long before the SES light tells you there's a problem. Heck, I can tell an oxygen sensor is going bad by reading the sensor's output on a scanner long before it even throws a code. to make matters even more complicated, the sensor also contains a portion that is a referance to the outside air as a comparison. if that portion becomes chemically fouled, kiss it goodbye as well. It's easy for that to happen with something as simple as PBlaster sprayed on a nearby fitting or bolt and it gets on the sensor. All of the above scenerios will throw an SES light. Cleaning the bulb may only work in 25% of the cases.


As cheap as an oxygen sensor is in the grand scheme of things, since you have to pull it to clean it, why not just replace it so that it's good for another 75K miles? Yes, I've cleaned a sensor and had it function for a little while longer out of necessity, but now you are into doing the work twice. I suppose it all depends on what shape you wish to keep your car in.

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[pandorasboyfriend]

Heck, I can tell an oxygen sensor is going bad by reading the sensor's output on a scanner long before it even throws a code.

Joe, when you read the sensor's output do you go by the volts?.
I'm using a OTC Matco Determinator scanner. I was told that if the O2 sensor is good the scanner(graph) will show the o2 flickering lean-rich, lean-rich, lean-rich etc very fast. So, the slower the reading is, the worse the sensor gets. And if the read out is stuck on rich or lean, then it is defintely bad. Does this sound correct?

As cheap as an oxygen sensor is in the grand scheme of things, since you have to pull it to clean it, why not just replace it so that it's good for another 75K miles? Yes, I've cleaned a sensor and had it function for a little while longer out of necessity, but now you are into doing the work twice. I suppose it all depends on what shape you wish to keep your car in.

At the same time if the outter and inter electrode part of the bulb is clean free of foriegn matter then why go buy one?. If it is beyond cleaning then I can see replacing it.

Let me use a battery for example. If the battery isn't putting out 12volts "due to corrosion" of one of the terminals, you don't go buy a new battery. Just clean the terminal(s).

Maybe i've just been lucky, because I haven't replace a O2 sensor in probably 15-16 years on a '95 T/A with more than 140K miles.

[Joe 1320]

Joe, when you read the sensor's output do you go by the volts?.
I'm using a OTC Matco Determinator scanner. I was told that if the O2 sensor is good the scanner(graph) will show the o2 flickering lean-rich, lean-rich, lean-rich etc very fast. So, the slower the reading is, the worse the sensor gets. And if the read out is stuck on rich or lean, then it is defintely bad. Does this sound correct?
.

Yes! However, you don't have to be stuck in one range or another. When an 02 sensors begins to look a little lazy, that's the time to start looking at what caused it.

Let me use a battery for example. If the battery isn't putting out 12volts "due to corrosion" of one of the terminals, you don't go buy a new battery. Just clean the terminal(s).

Maybe i've just been lucky, because I haven't replace a O2 sensor in probably 15-16 years on a '95 T/A with more than 140K miles.

The battery analogy would be applicable if we were talking about the sensor's harness. Since you are on the battery anaolgy, think of the battery having one bad cell. The whole battery still puts out decent voltage but it won't sustain a high amp load.

140K miles on the stock sensor is admirable. That's how they are supposed to work, often times they don't. Heck, when I first got my T/A the SES light went on after 200 miles, it was reset and it kept coming on. Back to the dealer and it was due to a bad oxygen sensor on the passenger side.

Edit: forgot to mention, the voltage will be in millivolts.

[Injuneer]

Joe's got it right.... a little bit of carbon buildup, and you MIGHT be able to clean it (how do you know you aren't damaging the zirconium substrate or the platinum layer?). But the sensor will "self clean" that kind of buildup. Its contamination from things like lead and silicone that cause the serious damage, and slow the sensor's response down, and that's not going to be undone by "a needle from grandma's sewing kit". I don't even see how you can insure the cleaning is complete when sticking a needle through a few tiny slots. And how do you clean the inside of the thimble, which must be exposed to atmospheric air to allow the cell to generate the voltage?

As the sensor slows down, its no longer able to accurately feed the PCM the info it needs to control the A/F ratio. Any slowing down causes loss of efficieny and performance as hysteresis increases. The factory sets the PCM to set codes when the transition time from rich to lean (or lean to rich) exceeds 100 milli-seconds. If you don't have OBD-II in your 4th Gen, you don't even have this warning to protect you.

Contemporary 4-wire sensors are designed for a 100K mile life. Many survive beyond that, so attributing 140K mile life to cleaning with grandma's needle is sort of naive at best. Why risk fuel mileage and performance for a $35 part (or two of them)?

[pandorasboyfriend]

Ok, one more question and I'll shut up:

What if your catilytic converter stops up and you throw a SES to the primary O2 sensor. You replace the O2 sensor. Basically you've replaced an O2 sensor that didn't have to be replaced, because the Caty was the problem all along. right or wrong?

[dochidalgo]

Well, You decide:
OBDI....2 precat O2 sensors....if the cat is faulty you will not get a SES light warning you about it...You'll have to guess the cat failure thru indirect symtoms: lack of power and low fuel mileage...

OBDII...2 precat AND 2 post cat O2 sensors.....these will warn you about a bad cat performance plus the symtoms mentioned already...

Take care
dochidalgo

[pandorasboyfriend]

I've got it.

Thanks for the info guys.

[Injuneer]

Ok, one more question and I'll shut up:

What if your catilytic converter stops up and you throw a SES to the primary O2 sensor. You replace the O2 sensor. Basically you've replaced an O2 sensor that didn't have to be replaced, because the Caty was the problem all along. right or wrong?

Why would a plugged cat "throw a SES to the primary O2 sensor"? With any code, you don't just look at the code and say "oh, its an O2 sensor code, I think I'll replace it and solve my problem". Anyone with any mechanical knowledge knows that the code is just a symptom of the problem, and the problem may be located elsewhere. That's why they have so many specific O2 sensor codes.... each one identifies a different symptom, and allows you to backtrack to the source of the problem. Replacing an O2 sensor because you have an O2 sensor code is no better than the dealer mechanics we curse so frequently for playing "parts replacement roulette" with our money.