How many O2 sensors...

[Paragongx]

Are on the Bonneville? I was thinking 3 but I'm not sure now. RockAuto has two different Denso O2 sensors listed (2344018) is labeled front and (2344087) is labeled rear. Looking at the pictures, it looks like they have different connectors. Is the one labeled front for the ones pre-cat and the one labeled rear post-cat? Would it be best to replace all of them at the same time? Thanks.

[J Wikoff]

The rear sensor doesn't do anything but tell the computer if the cat is ok. Good or bad, that sensor won't affect how your car runs.

[Paragongx]

So then there are 2 sensors pre-cat, one for each bank? If so are they identical? I had to have my cat changed out last year, ended up changing out the entire exhaust system, thank you federally mandated 8 year, 80,000 mile warranty!! Think the post cat is still OK?

[J Wikoff]

I think the fronts are the same... wait for someone else to confirm that there are two pre-cat sensors.

[Mechanical Mike]

Up to 2000 there is only one before the cat. I believe it's the same for the 2000 & newer 3800's.

[bonnevillain]

There are only two sensors. The front 02 sensor right by the downpipe after the front and rear manifolds come together, and one in the rear that basically only monitors the effectiveness of the catalytic converter, and has no effect on anything. Be sure you get one for the correct year.. The newer ones (2005 for sure, and possibly 2004) will output a constant 450mv in your car.

[Paragongx]

Great. Thanks. I would've just popped the hood and checked but wife has the car and I'm trying to get all parts I need ordered so they're here by this weeked. She's gonna be gone for a week and change so I've got lots of wrenching to do on all three of our cars.

[00Beast]

Correct, there are only 2 sensors. The pre-cat is on the rear manifold, and is easiest to get at from the top. It took a breaker bar, u-joint and a long extension to get mine off with an O2 sensor socket, lol. I had to replace my rear one because it threw a code, but if yours isn't, leave it. To replace it, you have to drill out the rivets that hold the shield on to get at the connector, then re-attach shield with short sheetmetal screws. Only replace if needed. The difference is that one has a male connector, and the other has a female, although I can't remember which is which. Order the one labeled Front.


You know not to get a Bosch, correct? AC Delco, Denso or NTK only.

[Paragongx]

Good to know on the rear one. I won't worry about it. Yeah I noticed there seems to be a lot of bad blood between our cars and Bosch stuff. I'll be going with the denso on the O2 sensor. Thanks

[LeSabre in Buffalo]

Also, when the car is warmed up, hit the front O2 with a spray of PB Blaster. The heat will help draw the Blaster into the threads, making it very easy to replace. On my 1999, I replaced the front O2 sensor in under 30 minutes, including renting and dropping off the O2 sensor socket.

[Plasmaburn]

To replace it, you have to drill out the rivets that hold the shield on to get at the connector, then re-attach shield with short sheetmetal screws. only.

is there no other way to get to the plug end ?

[00Beast]

Nope. It's inside the shield that is riveted into the floor, unless you wanna cut the floor up. Drill out the rivets and re-attach with sheet-metal screws.