D5 215 fault code

[dhr90]

I’m getting poor mpg (an indicated 30mpg at 70mph on the flat, no load, no wind and tyres at 38psi) from my d5, have done for quite a while now, maybe a year. In October after a service, a code was found and the Volvo independent removed, cleaned and refitted the oxygen sensor. This seems to have solved an issue where the car would go into a sort of limp mode, reducing speed, but still revving freely when in kickdown no dashboard lights would come up.

I’ve got a Bluetooth dongle, and car scanner pro repeatedly shows the following code, even after clearing: P2A00(36). Heated oxygen sensor 1, bank 1. Am I right in thinking this is for the first exhaust sensor? If so is this easy to get to if jacked up? Or can it be a pain to replace?

I have also had a code of P0544(00) come up once, this has not reappeared after it was cleared. Is this a different sensor in another location?