Where's the 02 sensor

[luisbe]

I need to replace the 02 sensor, Does anyone know where it is located?
Thank you.

[gmtech1]

Some info on what you are working on would be helpful. I will go with a 98 transoprt. There are two sensors, one is in the rear exhaust manifold, and one is behind the catalytic converter.

[Tech II]

You don't say the year....if OBD I, only one O2 sensor......if OBD II, it has two.....

The first one is located in the exhaust pipe between the ex manifold and the cat.....the second is located in the pipe just after the cat....

However, this being a van, it's buried between the firewall and the rear of the engine....

[luisbe]

Sorry, 1994 Trans Sport 3.8L

[luisbe]

is there any way to get a picture of it somewhere?

[LMP]

it is at the rear of engine, you can seeit from under the car. it is bolted to the rear exhaust manifold, ..a bit out of sight in this picture
www.avigex.ca/xport/rearplugs.jpg you have to remove the exhaust shields (removed here) to get a better look. I think (not sure) you would need a special socket to unscrew the O2 sensor.
By the way, mention car model, engine type, model year at begining of all new threads. Not all will check your previous threads to find the relevant info.
ALso....what conditions tell you you have to change this O2 sensor....

[luisbe]

I idles not too bad when cold but while warm it stalls on traffic lights and idling becomes irregular, it spends tons of gas (full tank/250km).
I've read many articles on internet those are symptoms of a bad 02 sensor.

[luisbe]

Also it smells like rotten egg from the exhaust.
Do I have to unscrew the beginning of the pipe and check inside?
Thank you

[LMP]

mmm...that would also be symptomatic of an injector that is blocked opened. Start engine and unplug injectors one at a time . Disconnecting the culprit would improve idle...by the way, do you have codes?....ahhh...quite hard to get them in '94....known as OBD 1 1/2....

[LMP]

Also.....an opened coolant temperature sensor can fool the computer into thinking the temperature is very cold and it would make the mixture too rich trying to compensate. Also, notice the O2 sensor enters the computer computation only once engine is warm. When engine cold, it runs on "default" values that ignore the O2 sensor.
It "can" still be the O2 sensor but do not ignore more simple options in the first place.
..does your Check Engine Light show ?

[luisbe]

yes, it does, after 80km/hour starts showing.

[luisbe]

So what do you suggest? Is there any way to read codes?

[luisbe]

sorry, how do I open the injector?

[luisbe]

BTW I have theses codes but I do not know how to do to get them in the vehicle.
(Attached picture)

[Tech II]

Has the Check Engine light been on?

Rotten egg smell means the vehicle is running rich.....

Is this vehicle misfiring?

As for reading codes, you could be in a transition year....do you have a 16 or 12 pin ALDL? If 16, no flash codes available....if 12 pin, you ONLY have flash code capability if there are pins in the "A" and "B" connectors....chances are on this year you don't.....because it is a transisition year, many scanners can't read the codes in this vehicle...it would take a GM scan tool, or an expensive advanced one to read them.....

Yes a contaminated O2 sensor could cause the vehicle to run rough......however, just changing the sensor may not solve your problem, because whatever caused that sensor to go bad(for example, running rich), is still there and will contaminate the sensor again......

Last tuneup on vehicle?