Oxygen Sensor

How do you replace an oxygen sensor in a 1997 Cadillac Deville? Where is it located?

the car has 4 of them, 1 on each side just below the exhaust manifold b4 the cat. and 2 after or down stream from the cat. is the check eng. lite on? if yes what is the code

yes it is. the code is PO139

Drivers side after the catalytic converter.

i had a mechanic that i work with tell me it was on the passenger side. how can you tell which side it is on?

I guess it depends on how the engine is mounted. P0139 is bank 1 sensor 2. You can confirm that here.


Bank 1 is on the side of the engine where the number 1 cylinder is located. If the engine is mounted longitudinally, that is fore and aft, typical for a rear wheel drive vehicle, then bank 1 is on the drivers side. If the engine is mounted sideways and the front of the engine is on the passenger side, typical for US designed front wheel drive cars, then bank one is on the radiator side of the engine compartment. The exhaust pipe for bank 1 could run down either side of the vehicle, that would be up to the designers.

alright. is this a relativively easy job? i have done a lot of work on cars but never an oxygen sensor

A lot depends on where the connector is located. Some cars have the connector near the sensor, but the issue with this is that sometimes water gets into the connector because of its exposed location. In some cases, the first thing to do for this code is to disconnect the plug and clean the contacts, then put it back together and drive for awhile to see if the code clears.

Some cars route the wires up into the cabin, usually next to the tunnel on the passenger side and make the connection under the dash. Needless to say, these are a bit more difficult to replace because the carpet has to be pulled up and that might mean removing the console. My experience with GM vehicles that there is no job too easy that their engineers can’t make very difficult. And Nissan must send their engineers to GM for training in that area.

ok. im gonna give it a shot tomorrow afternoon. hopefully all goes well but if not ill be back on here. i just dont wanna take it to a mechanic becuase its only a $70 part but if i took it to a mechanic it would turn into a $300 job

If the connector is exposed under the vehicle, I would clean out the connector before spending the $70.

You can expect a fight getting the old one out…Use the proper size wrench. If one is bad, the other can’t be far behind. You should replace all 4 of them, but at least replace the rear pair…The higher off the ground you can raise your car the better…Do NOT crawl under there with just a jack(s) for support…Jack-stands are a MUST…