astrozoom

I recently received the CEL of P1405 (Differential pressure feedback sensor - upstream hose off or plugged) and P0136 (Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2). I recently replaced the rear 02 sensor. The connection seems to be fine. I am not sure where exactly the Differential pressure feedback sensor is located? Any help with that would be great along with any help on what the issue could be. I looked, and I didn't see any lose hoses. I am not sure where exactly the differential pressure feedback sensor is, so I might have missed it as well. I did a search for this, and I was unable to find anything. Thanks for the help.