P0150-35-10 Oxygen Sensor!

[Philws4]

Did a scan on mine this evening and got the code :
16534 Oxygen(Lambda) Sensor B2 S1 Malfunction in circuit
P0150-35-10- Intermittent.

I cleared the DTC and went for a spin then checked again and so far not re-appeared but only a matter of time i guess!

Is this just a case of replacing the EGT,and on which side? ( I bet it's the awkward one, N/S!)

Also had 18048-Internal Control Module EEPROM Error
P1640-35-10 Intermittent WTF is that all about!!!!
This cleared ok and did not re-appear.

Any Ideas?