I am the father of a 22 yo who is in love with his 1999 Cadillac Deville. It is in fantastic shape for a 99 with 100,000 miles on the odometer. Yesterday the check engine light came on and Auto Zone diagnosed it as a failed 02 sensor. They told me it was the one on the front of the engine as your facing it. The engine is the Northstar V8 just in case. I looked all over and could not find the sensor on the front of the engine. If anyone has a clue or knows where the thing is located please let me know. On the net they say there are four 02 sensors could not google or bing locations. I am hoping someone here can help.

Thanks from a grateful dad.

 

They are located in the exhaust. You have to know witch o2 sensor is bad. There are 2 for each bank, bank 1 sensor 1 or 2, bank 2 sensor 1 or 2.

 

I found it; not easy but it is done. It was the first one on the bottom drivers side front of engine. Had to take all the plastic off the bottom and get the car up on stands. The one that was in there was very loose, wonder if that caused the bad reading. Replaced it and on my way to have the code reset. Thanks again.