2.5L ('98-'01) Oxygen Sensor Misinformation

[purple_fluffer]

I can't believe all the web pages I read and videos I watched where they say this stuff with a straight face. ima' have to set this straight. so the 20 people that read this know better, and the other 3841,578,4599,46,898 people on the internet will never hear about it.

IT WILL BE STUCK

when you look up how to replace your oxygen sensor, many sources say it will be stuck so bad you need a special wrench, penetrating oil, and a blowtorch. in fact the wrench has a slot in it for the wires and you have to hold the slot together with an O-ring clamp or it spreads apart and the socket slips, because it's so hard to turn. because exhaust parts are like that.

my experience at the junkyard removing 4 used O2 sensors was that they were so easy to remove, all that was needed was a 7/8 wrench and a tap with a hammer. one was so easy after it broke loose it unscrewed the rest of the way with my fingers.

maybe they are stuck that bad sometimes. I did 4 and they weren't. without the fender skirt they are a breeze, that's about the easiest thing to remove on the whole truck. without removing the fender skirt, the special socket is needed because it'a a slotted crow's foot and you can use it with a few socket wrench extensions on a breaker bar to unscrew the sensor from above. and it's still easy, it won't be stuck.

WHAT THEY DO AND HOW THEY WORK

it doesn't actually detect oxygen molecules. there is nothing chemical about it, and that would be impossible, because it would get too dirty too fast, and the exhaust is 800-1200 degrees F sometimes 1500 F.

it has a thermistor inside that protective metal casing with slots on it that you see on the end. a thermistor is a resistor that has more resistance when hot and less resistance when cold. every electronic item in the world that senses temperature uses a thermistor.

the truck's computer sends an electrical current through the thermistor so it can measure resistance, which tells it how hot the exhaust is, which tells it if the air/fuel mixture is too lean (hot) or rich (cold) compared to what it should be, given the RPM's etc.

YOU CAN CLEAN IT

first off, cleaning it won't help much, because it's not an oxygen molecule detector that needs cleaning. it's a lump of ceramic that has variable resistance depending on temperature. cleaning won't have much if any effect. unless it's really gummed up.

second, the problem is usually that the pre-heater in the sensor body is broke, melted, etc and that's why it pops an error code, causing the computer use preset, default values the whole time the engine is running, instead of actually using the sensor. cleaning won't do anything. it's broke. it needs replaced.

the second most common problem is that it is worn out and doesn't read right after so many heat/cool cycles. they last 100,000 miles. cleaning won't help that either.

what's the pre-heater for?

the pre-heater is there to heat the sensor up to operating temperature (at least 800 degrees) when the engine has just started and is still cold. also, during that phase the computer uses it as a test to see if it's going to work at all. if not it uses default values instead and ignores the sensor. the heating element is a long peice of wire taking up most of the length of the sensor body, and continues into the sensor itself to heat it up. otherwise the sensor would only be 1" long instead of 4". and that's why it has 4 wires instead of 2, for the heating element.

DON'T TOUCH IT OR DROP IT

yes you can touch it. the metal cover is for protection, it's not the sensor itself. even if it was the sensor itself, big deal. touching a ceramic resistor won't do anything to it. however, dropping it might crack or break the ceramic from the shock of g-forces.

 

[franklin2]

A O2 sensor is NOT a thermistor. When it is warm enough, it actually generates it's own voltage like a battery. It's a very small voltage but it can be read with a decent digital voltmeter set on DC volts.

And yes they can get very stuck. I had to replace the exhaust system on a vehicle once because of it. I got the sensor out, but no amount of thread chasing and tapping would make the new one go in. Something happened to the threads inside the bung. And that stainless alloy they use now was so tough the threads would not clean up.

 

[rumblecloud]

I'm happy

...my experience at the junkyard removing 4 used O2 sensors was that they were so easy to remove, all that was needed was a 7/8 wrench and a tap with a hammer. one was so easy after it broke loose it unscrewed the rest of the way with my fingers.

While I am happy you had an easy time removing and replacing your O2s, they will get "stuck." Welded in place is more descriptive.

 

[SenorNoob]

I know about the stuck. When I put the 1st engine in, I used a new O2 sensor. It's threads were coated in nickel anti-seize. When I changed the engine again ~10 years later, it was so stuck that I had to replace the y-pipe. I had the pipe off, in a shop vice, wires cut on the sensor and an impact socket on it. Tried a 1200 lb-ft Dewalt impact, it just laughed. I got a 3/4 breaker bar and long (6ft) cheater bar and the pipe crushed like a beer can. Sensor never moved in it's threads.

 

[Curious Hound]

I can't believe all the web pages I read and videos I watched where they say this stuff with a straight face. ima' have to set this straight. so the 20 people that read this know better, and the other 3841,578,4599,46,898 people on the internet will never hear about it.

IT WILL BE STUCK

when you look up how to replace your oxygen sensor, many sources say it will be stuck so bad you need a special wrench, penetrating oil, and a blowtorch. in fact the wrench has a slot in it for the wires and you have to hold the slot together with an O-ring clamp or it spreads apart and the socket slips, because it's so hard to turn. because exhaust parts are like that.

my experience at the junkyard removing 4 used O2 sensors was that they were so easy to remove, all that was needed was a 7/8 wrench and a tap with a hammer. one was so easy after it broke loose it unscrewed the rest of the way with my fingers.

maybe they are stuck that bad sometimes. I did 4 and they weren't. without the fender skirt they are a breeze, that's about the easiest thing to remove on the whole truck. without removing the fender skirt, the special socket is needed because it'a a slotted crow's foot and you can use it with a few socket wrench extensions on a breaker bar to unscrew the sensor from above. and it's still easy, it won't be stuck.

WHAT THEY DO AND HOW THEY WORK

it doesn't actually detect oxygen molecules. there is nothing chemical about it, and that would be impossible, because it would get too dirty too fast, and the exhaust is 800-1200 degrees F sometimes 1500 F.

it has a thermistor inside that protective metal casing with slots on it that you see on the end. a thermistor is a resistor that has more resistance when hot and less resistance when cold. every electronic item in the world that senses temperature uses a thermistor.

the truck's computer sends an electrical current through the thermistor so it can measure resistance, which tells it how hot the exhaust is, which tells it if the air/fuel mixture is too lean (hot) or rich (cold) compared to what it should be, given the RPM's etc.

YOU CAN CLEAN IT

first off, cleaning it won't help much, because it's not an oxygen molecule detector that needs cleaning. it's a lump of ceramic that has variable resistance depending on temperature. cleaning won't have much if any effect. unless it's really gummed up.

second, the problem is usually that the pre-heater in the sensor body is broke, melted, etc and that's why it pops an error code, causing the computer use preset, default values the whole time the engine is running, instead of actually using the sensor. cleaning won't do anything. it's broke. it needs replaced.

the second most common problem is that it is worn out and doesn't read right after so many heat/cool cycles. they last 100,000 miles. cleaning won't help that either.

what's the pre-heater for?

the pre-heater is there to heat the sensor up to operating temperature (at least 800 degrees) when the engine has just started and is still cold. also, during that phase the computer uses it as a test to see if it's going to work at all. if not it uses default values instead and ignores the sensor. the heating element is a long peice of wire taking up most of the length of the sensor body, and continues into the sensor itself to heat it up. otherwise the sensor would only be 1" long instead of 4". and that's why it has 4 wires instead of 2, for the heating element.

DON'T TOUCH IT OR DROP IT

yes you can touch it. the metal cover is for protection, it's not the sensor itself. even if it was the sensor itself, big deal. touching a ceramic resistor won't do anything to it. however, dropping it might crack or break the ceramic from the shock of g-forces.

While I'm glad your experience with removing these has been good, it is not a very large sampling to call "average" or to use for debunking the experiences of others. Those who love in northern regions where salt and brines are used on the roads in wintertime often have much worse experiences with almost any fasteners andbparts on the exterior parts of their vehicles, due to rust and corrosion. I have always had a relatively easy time with these, as well. But, they do, indeed get very, very stuck. A crows foot (offset open-end wrench that can be put on a ratchet) or the slotted socket (not synonymous with "crows foot") are very useful tools and often necessary.

As for how the sensor works... you are wrong. Here is a link to some information posted by Delphi, one of the common manufacturers of these sensors and many other automotive parts.

Making Sense of Sensors: The Oxygen Sensor

The oxygen sensor, otherwise known as the O2 sensor, does what its name suggests – it measures the amount of oxygen in the exhaust. While this may sound like a fairly modest...

www.delphiautoparts.com

Happy wrenching.

 

[pjtoledo]

I have also found they can be easily removed, with a 2 foot long pipe wrench.
that method guarantees the need for new O2 sensors.
I have also taken them out piece by piece and surgically removed the thread remnants.

rust belt you say??? Oh yeah.

once had an engineer explain the output in detail. the transition from flat to ramp is where the output matters.
the transition is actually a tight curve.

EDIT: one more thing, why,why,WHY did some moron design these so that a 7/8 box wrench won't fit over the connector???? snip-snip

 

[Snoranger]

You’re welcome to come up here (I say up, because I assume you’re in the south) and try to remove an O2 sensor from any of the trucks in my fleet. Just keep in mind that we are a government agency responsible for plowing and salting 621 miles of roads.
I can tell you that about 1 out 20 will come out without ripping the threads out of the exhaust… even with heat.