: Having trouble locating o2 sensors

05-18-10, 05:41 PM
My car is throwing these three codes PCM P0135, PCM P0144 and PCM P0155, and which after checking online it tells me that the codes mean three of my oxygen sensors are bad, but I am having the hardest time finding them. Can someone tell me where they are located? Any diagrams available that I can see visually?

05-18-10, 06:01 PM
Pretty sure you have 4 - one on each exhaust manifold, one downstream before the cat, one after the cat. I doubt 3 O2 sensors went bad all of a sudden - I think you have a different problem - hopefully you have access to a FSM or Alldata?

05-18-10, 06:13 PM
Well they didnt all happen suddenly, the P0135 code has been displaying on my dash for around 6 yrs but because I rarely drive the car I have not got around to fixing it, until recently when my check engine light came on and i checked the codes to see if it was the same one and noticed the other two popped up.

05-18-10, 07:11 PM
3 O2 sensors "bad" sounds like a vacuum leak, but.............

The diagram of the sensor after the cat - you have another just in front of the cat (your cat flange is different) as well as at each manifold.

06-24-10, 09:11 AM
I found the rear O2 sensor bank i on top of the exhaust manifold now how in the hell do I get it off? Talk about a plumbers nightmare!!! It looks more difficult than when I installed the blower motor and its right under it.

06-24-10, 09:26 AM
Work over the top with long extension tools (let the sensor soak with a shot of PB Blaster overnight) or get the car up on a hoist and lower the rear of the cradle a bit.

Either way, not one bit of fun..............there was just another thread on this in Seville or Deville maybe - quite a devil of a job.

06-24-10, 10:49 AM
Now that I've had a closer look at it, its not too difficult removing it since I have to remove the blower again anyway. I'm thinking a long extension possibly with a magnetized oxygen sensor tool will help to seat it properly OR I can pack the socket with tape to ensure that the oxygen sensor remains in the socket if I cant get a magnet. I can just break the top off the old one to help with the removal. The DIFFICULT part from what I can tell is getting to the wiring

06-24-10, 03:12 PM
I think if I had to do it, I would try dropping the rear of the cradle, but I've dropped the cradle on two different Cadillacs before, so I don't find it at all intimidating.

I completely dropped the cradle on my'97 ETC to do the HG repair, and I partially dropped the front of the cradle on the 2000 DTS twice - once for the motor mount, another time for the heater hoses and rear ignition cassette and plugs. Dropping or partially dropping the cradle really makes a lot of sense in our cars, and is easy and not scary at all, once you try it. Just use some common sense in what you're doing, and you won't have any problems.

06-24-10, 10:52 PM
Sure, hey I'll jump in again. I love these threads.

O2 sensors don't' go bad. Ok they can but it's like one in 10 zillion chance. They just don't fail unless something causes them to. Usually when you start getting codes for O2 sensors it's because the car is either running so rich or so lean that the PCM can't compensate for it.

The condition is caused by something else causing the sensors to get false positive readings, throwing them out of spec, in turn throwing codes.

If you drive around rich for 2 years or so you may get an O2 sensor to fail.

Look for, vacuum leak, clogged cat, bad injector, something else but I really doubt it's the sensor itself.

06-25-10, 06:36 AM
Piece of cake with plenty of room to access once the blower is removed, and I removed the blower easily by removing the 4 bolts from the back of the unit.

http://img338.imageshack.us/img338/921/img00104cd.jpg (http://img338.imageshack.us/i/img00104cd.jpg/) Uploaded with ImageShack.us (http://imageshack.us)

06-25-10, 01:25 PM
Looks good - thanks for the photo - I thought I'd read the blower motor was difficult to R and R.