How many oxygen sensors are in a 04 Buick park Ave ultra? and where?

I took my car to AutoZone because I had the Service Engine Light on. They told me that an oxygen sensor had no activity. So I looked under the hood and under the car and only found two sensors. Autozone told me that there were four. 2 upstream and 2 downstream. Buick sure hid them well. Does any one know where the other 2 are?|||If you have dual exhaust, there can be up to 4, depending. If there are, you will find one fore and aft of the catalytic converter, on both sides.





Keep in mind that AutoZone only does the scan in an attempt to sell parts, and that it's only as good as the person who does it.





If you have the scan done by your own mechanic, they can pinpoint which one (if any) is bad.





You'll get something like this: P0140 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2), which tells you drivers side, aft of the converter.





And it could be your 04 only has two, I don't have the book in front of me at the moment, but your own mechanic will know when you go see him to get it scanned.|||How can they tell if a sensor had no activity. Those cheap code readers they use can't actually tell you that. My guess is if you try to replace one of the sensors you are throwing your money away.





When you get a FREE diagnostic you do get exactly what you pay for.|||The other two will be behind the cat converters...they will be halfway under the car, so I don't believe you will be finding them with a quick peek.