I have a 04 Chrysler Concorde 3.5L. Getting a Code P0138.
is this the downstream o2 or upstream?
passenger side??

 

Bank 1 is the right side of the motor facing forward to the water pump/timing belt and also holds cylinder 1 - so yes passenger side

Sensor 2 is the downstream O2 sensor after the cat. Sensor 1 is the upstream O2 sensor before the cat.

Use only OEM/NTK O2 sensors, others do not play well (no Bosch, ever)

 

Might want to consider replacing both the up and downstream sensors. The computer determines how well the cat is working by comparing the signal from the upstream and the downstream sensors. The ratio tells the computer what it needs to know. As sensors age they give different signals but the ratio is what's important. Replacing one sensor can throw off the ratio and may fool the computer into thinking that the cat is bad. As long as you're messing around down there, you may just want to swap out both of them to save the return trip. As you thread out the old sensor, you may get little chunks of rust in the threads which can make it very hard to continue on the way out. If you feel it jamming, try threading it back in a bit in hopes that the chunks will fall away.

 

Thanks both of you for your help