I will start by stating that all 4 oxygen sensors were replaced on my car ~ 1 year ago.
A few months back I started getting a CEL on my 986 Boxster. The code reported was P2096 (P2096 Signal Delay Time for Oxygen Sensor Ageing - Above Limit)
I cleared this error and after ~150 miles the CEL reappeared once again with the same code. I cleared it but it reappeared once again after ~100 miles. Unfortunately, this did not point me towards which of the 4 oxygen sensors was reporting the problem.
The fault reoccured 2 weeks ago (P2096). This time I decided to swap the 2 post cat oxygen sensors to see if that resulted in a different error code. IT DID! After 50-100 miles the CEL reappeared. This time the OBD II code was P2098.
P2098 Signal Delay Time for Oxygen Sensor Ageing, Bank 2 – Above Limit
My next step would be to replace the post cat oxygen sensor on Bank 2. Does anyone have a similar experience or any further suggestions on diagnosing the fault. Could the oxygen sensor fault codes be a red herring for some other problem with the exhaust system?
Generally if the converters are under performing there are specific error codes for that condition and while my info on those error codes is sparse I do not necessarily get the feeling the converters are at fault.
Also, there are error codes related to aging O2 sensors: slow response, weak response.
BTW, not sure where you are getting the descriptive test for those DTCs.
My references show:
P2096: Post catalyst fuel trim system too lean, bank 1.
P2098: Post catalyst fuel trim system too lean, bank 2.
Did you obtain any freeze frame data with one or both of the above error codes?
Did you get any other error codes like misfires?
Groping in the dark the errors can arise from an exhaust gas leak, #2 O2 sensor problem, and about a zillion other failures.
Since you replaced all 4 sensors a year ago I would have to wonder if the sensors you chose are sub-par or if perhaps if thread lube was used upon the sensor threads that the wrong type of thread lube was used.
But eliminate an exhaust system leak before you throw money at new sensors.
In fact, before you throw money at anything other than crawling under the car and checking for an exhaust system leak, throw money at an OPC.
You're probably money ahead by having a OPC diagnose this for you. There are probably 20+ test steps that eliminate IAT sensor, ECT, intake air leak, MAF, fuel pressure, and so on.