Merecdes Benz C200K,2001,code:P210D,P2031

My car is Merecdes Benz C200K, 2001, petrol, 40,000 miles.
Last week while coming back from Heathrow, I noticed Engine management light but the dashboard said no malfunction. The car ran normally so I kept driving and next day got it checked.
It revealed 5 codes which were reset by the mechanic.
For next 4 days, everything was normal but then Engine management light came back and this time 2 codes were repeated. The codes are
P210D--Mixture format-Fuel trim
P2031-- Oxygen sensor upstream catalytic convertor

The car is not losing power and running normally. Is it the Air flow sensor fault or simply Air filter needs changing or any other fault?

Parag
singhal; Those trouble codes are not US compliant, but from the description, sounds like you have an Oxygen sensor issue, which would account for both codes. The upstream oxygen sensor tells the computer the air/fuel mixture and
compensates accordingly. Those codes don't tell me if it is seeing a rich, or lean. mixture. Yes, a plugged air filter could cause a rich condition. This is not something that you want to ignore. A severe rich or lean condition can cause engine damage.
Loren
SW Washington