Where's the 02 sensor

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

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.

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....

Sorry, 1994 Trans Sport 3.8L

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

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....

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.

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

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....

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 ?

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

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

sorry, how do I open the injector?

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

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?

Last tune up was 5 years ago but it's been standing still for almost 1 year and a half, just making it idle once every 2nd week; that was until last year, since then it's been running almost daily.
I have no idea about pins, I'm not a mechanic, just I cannot afford at this time to bring it to one of them.
What would you do for tuning it up?
I've changed all spark plugs and it passed emission test in May/2011.

''94 cannot flash codes nor can be read with an OBD2 scanner....There is a solution using an USB adaptor to a PC. It can be bought online and the software comes with it .
http://www.aldlcable.com/sc/details.asp?item=aldlobd1u
read the notice about 12/16 pin connector. COnnector is at bottom of instrument panel, near hand brake release. Verify number of pins.

MOst of the time, it tells consequences, not causes.....so it might not help that much anyway

ANyway, you have to probe options.
INjectors can be electrically unplugged..just pull the connector at top of injector...easy on front injectors.....more of a problem for the rear...just hope for a miracle up front....but you know my signature...

Thank you for the info, I'll make a picture of mine later.

here is my '93 connector.
http://www.avigex.ca/xport/plug.jpg
Most probably you have also this 12 pin connector but without pin A or pin B

That's exactly what I've got.

That's exactly what I've got.
....details..details....my guess is "almost , but not exactly".....pin B does not exist in '94

It seems the two top pins are the same. Like little white dots at the right top corner.

Then two pins on the bottom, from right to left first and third.

It seems the two top pins are the same. Like little white dots at the right top corner.
Well in that case, this might be a first series '94.....and maybe....just maybe you could try flashing the codes
..but maybe they just kept using leftovers plugs from '93 with pin B unconnected.......because some '94 were reported like this
--------------
| o o o o o o |
| o o o o o o |
--------------


unfold a small paper clip imto a U , insert into A ans B then turn key ON....if the CEL starts flashing .....verify this:
www.avigex.ca/xport/readingcodes.jpg

...??? Fonthill...near St-Catherine?...

Yeah, near St Catharines and Niagara Falls.
I'll do that tomorrow then I'll come back with the result.

I remember years ago in some shop somebody read that with a scanner then they replaced a sensor on the front of the air filter case (MAF?). It was idling rough at that time too.

Well, finally here is the picture I told you, it seems pretty clear on how it looks.

Well, finally here is the picture I told you, it seems pretty clear on how it looks.

TRy the paperclip into A and B....but though it does have A and B, ...it has also many more pins than my '93.....I doubt it will flash the codes

Ok, I'll give it a try tomorrow during daylight. Hope it works. Thank you!

If you have a 94-95 with a 3800, you will not be able to flash codes due to the PCM used, there is no diagnostic " Flash " feature in the PCM... Must be read with an OBD1 Scan Tool capable of reading the 94-95 odd ball GM's...

Usually, when there is a "contact" in the "A" and "B" slots, there is flash codes......when one is missing, there isn't.....in this case, they are both there....

Ok, a question. What can it happen if I bridge it and there's not a data link?
Will it burn a relay or fuse or something else?
I mean, Can I confidently give it a try?
Thank you

No adverse consequence.

Ok, I dont understand this, here it goes in quantity of flashes until I got tired of writing it down.
3/2/2/2/3/2/1/2/2/1/2/3/2/3/2/3/2/1/2/1/2/1/2/3/2/3/2/3/2/1/2/1/2/1/2/3/2/3/2/3/21/2/1/2/1/2/3/2/3/2/3/2/1/2/1/2/1/2/3/2/3/2/3/3/2/1/2/1/2/1/2/3/2/3/2/3/2/1/2/1/2/1/2/3/2/3/2/3/2/1/2/1/2/1/2/3/2/3/2/3/2/1/2/1/2/1/2/3/2/3/2/3/2/1/2/1/2/3/2/2/2/3/2/1/2/1/2/1/2/...
What does it mean all that?

Of course I can do it all over again if it has any meaning.

Ok, I dont understand this, here it goes in quantity of flashes until I got tired of writing it down.
3/2/2/2/3/2/1/2/2/1/2/3/2/3/2/3/2/1/2/1/2/1/2/3/2/3/2/3/2/1/2/1/2/1/2/...............

What does it mean all that?

ALL codes are repeated 3 times....when all codes are read, it starts again....ad nauseam...

OK..I start with a 1/2 1/2 1/2 sequence ...which means "ready to read".
then 3/2/3/2/3/2 meaning 32...

then it starts again 1/2 1/2 1/2 ..meaning all codes have been read...the only trouble code is 32....a
nd it will repeat until you are tired.

well....32 is bizarrre...not listed in the '93 flash codes for the 3800...but in OBD2.....it could mean
"P0032 - Heated Oxygen Sensor (HO2S) Heater Circuit High Voltage Bank 1 Sensor 1"

'94 is bizarre, mixed OBD1 and OBD2 ...normally not flashes the codes...and here it gives a flash
code that could point to the first item you had suspected... but a "fail" code is often the consequence
of a problem somewhere else: it could be the O2 sensor itself....or the sensor is ovwewhelmed by a
blocked injector, for instance..

.. keeps me thinking the O2 sensor is NOT the culprit: only the victim : when O2 sensor has gone haywire, , the computer will NOT rely
on this reading and will use a "default mode"...running the engine with "average" values which offer an acceptable
performance...which is obviously not what you describe. If in fact the computer tries "average" values but another component is faulty,
it cannot achieve "average" performance.

Thank you for the help. Now I've got a question.
I've replaced the front, and visible, 3 spark plugs no long ago but I did not change the ones I've got to go under the van to do so.
Maybe, and just maybe, one of those is not good so you'd be right in that case that the code is deceiving since it could be an injector misbehaving.
I think my best bet now is replacing those spark plugs and see what happens.
Appreciate your patience and feedback.

May be you found my thread about the rear plugs.....there are other options but I found this one easier...with a pit to walk under....will try to locate the link...
...ahhh..here it is http://www.automotiveforums.com/vbulletin/showthread.php?t=599442

Thank you very much.

On OBD I, code "32" involves the EGR....

On OBD I, code "32" involves the EGR....
YOu are right..it shows on the '93 3.1 code list ..However, with the '93 3.8, EGR codes are 54,55,56 for the 3 section EGR valve, and with the proportional pintle valve used from '94, I do not know which OBD1 code would come, but OBD2 would be P1406....
This '94 is mind boggling....

luisbe....can you identify which EGR valve you have...?
this one http://www.avigex.ca/xport/egrphoto.JPG
or this one http://www.avigex.ca/xport/egrlin.jpg

Ok, Sorry about my ignorance on the matter.
What does EGR stand for?
and where is it in the engine, can I see it from the front of the engine?

After saying that, I don't think I have anything looking like to the picture on top in my engine although I cannot find it to compare either.

Exhaust Gas Recycling, one is answered (thanks google). Also says is located on the intake manifold.
May I ask you if I have to remove something to see it?
Thank you, and again do not forget I'm a neophyte regarding to all this so pardon if the questions sound too stupid at times.

It is on the front of the engine, clearly visible on the driver side, just past the valve cover.
Can you post a picture of your engine compartment....also...please can you confirm the car is actually a '94....maybe a photo of the whole vehicle would dissipate some doubts....

Ok, there it goes. My Vin says '94
(1GMDU06D3RT226248)

OK....my doubts were founded...yes, a '94 but this is not a 3.8...it is a 3.1
COnsequently, your code 32 is about the EGR valve....hidden on the intake manifold under the air filter on the 3.1...
ALso, this is a "throttle body injection"...not separate injectors for each cylinder. There are 2 injectors in the throttle body....physically comparable to the ancient carburator...
see that:
www.avigex.ca/xport/TBI.jpg

Still...I think a blocked injector in the TBI could explain your problem , that is, excessive fuel burn and poor idle and stall. THe EGR problem is accessory....

So it makes sense replacing the spark plugs first, am I right?

BTW As of yesterday my brake pedal went down to the bottom while driving. I pumped it and it brakes but some big trouble there. The only thing I've done so far is checking the reservoir but the level seems, strangely, normal.
This is another thread though, I know.
When I need the vehicle and the money is shrinking it happens.

Check for brake fluid leaks, front flex tubes can be suspected, but check all wheels.
There is no objection replacing the spark plugs..this is normal maintenance. Reaching the rear plugs from the top is easier on the 3.1....some remove the dogbone at the front and tilt the engine forward...
....

Well, at least I borrowed 2 ramps.
I have to forget about the spark plugs right now, the other issue seems more serious since it holds me from driving the vehicle, which I need for working purposes.
I'm appealing to you LPM who are THE GUY; I've read several threads back but I couldn't get something that lightens me so I'll post my problem here but eventually should be re post on a new thread. In that case I will.
Four or five months ago I lost my break so I went to the shop where they fixed a damage line going to the front left wheel (driver side). A week later both lights (ABS and brake) went on together. The guy revised the lines but everything seemed OK (according to him) and told me: "come next week for that problem". Money dried so I did not go but I continued driving while the vehicle was braking fine until a couple of days ago with the commented trouble of the brake pedal sometimes going all the way down but not every time. That's the situation as of today.
I've just checked all lines for leaking under the vehicle without seeing nothing wrong.
You mentioned something about flex tubes that I don't understand what it is or where it is situated, is it possible to get a picture somewhere or a diagram?
Appreciate not only your time but your patience.

BTW, the liquid in the reservoir continues at the normal fill despite of my pedaling several times looking for leaking.

I took 2 pictures:
Picture 1: Is this the dogbone?
Picture 2: Is this the servo?

Yes, this is the dogbone..but as you say, spark plugs are not that urgent at this time.
The other picture is the brake master cylinder and ther ABS unit. From what you describe, I think some air has been left in the brake circuit. That gives a soft pedal that goes farther than normal. That also pops the brake lights ON. Clearing the air implies "bleeding" the brake lines and wheel brake cylinders. Quite often the bleeders get stuck and if one does not use patience, one (or several) can be broken and this will lead to changing the corresponding brake cylinder/caliper....meaning lots of $$.
The "flex" lines I mention are those flexible rubber lines that go to the front wheel calipers..one of them was changed , according to your post.

Thank you.
It seems not too bad, at least for now.
Bleeding. I've been reading several threads regarding to, I understand there are 2 ways, is it so? One is the classic, by classic I know them mean one push the pedal and another opens a little valve. All I know is I've a friend some years ago by pressing down the pedal as asked but I did not see what he did.
I'm going to take a picture of the back of my van's wheel and ask you what's the little valve to use for that. I'll be back.
How to bleed a brake other than "classic"? What's easier?

Is this the little bleeding valve?

"All I know is I've a friend some years ago by pressing down the pedal as asked..."
That incoherent as written, I meant: I've a friend who I helped years ago by...

Yes that is the bleeder.
Well...there are some complicated alternate ways suggested with ABS systems, like pressure bleeding, even reverse bleeding..........but I've always gone "classic" without any problems. One note though: if the master cylinder has been left to go empty and air was introduced into the ABS unit, then there are also 2 bleeders on the ABS unit that you can use to purge the ABS first instead of pushing the trapped air all across the piping.
...ahh...close the bleeder cock while the pedal is at bottom.....or better, while it is being pushed down...not after it was released back up...

Thank you very much LMP, I'll do that tomorrow provided my wife helps me.:smile:

should ignition key be set to on before bleeding?