Peugeot 308 anti-pollution system fault warning

[Destination]

During the recent cold spell, I cleared the car of snow and ran it every few days until all was nice and warm and everything has been fine.
Car has 2500 miles on it, and is a petrol variant of a 308.

Today after returning to my house from beign away for 4 days, the snow is now gone, and the ice has all disappeared around here, ambient daytime was 10 degrees, so I sarted her up, she started first time, and ran, but a beep and warning light are on.
System states: anti-pollution system fault.
Engine fan was belting at full speed for 2 minutes after start, then quit, and all seems to be running fine, she idles revs fine, smoke minimal to begin then virtually nothing, heats to normal turnover temperature and runs soundly, but the engine light remains lit, and restarting brings the same message.

Anyone experienced or seen this? Was it related to cold spell?
Next course of action?

 

[Destination]

Yes I had read similar that a good drive might shift the issue but not actually clear the sensor light and then disconnecting and reconnecting the battery would do this.
Don't partilcuarly want to do it, as it isn't my vehicle, I'll try to find out where he bought it and give them a call to get it to them to have a look at things.

Seems common enough that the anti-pollution sensor on certain peugeots seems fickle.

I'll take it out for a good run and see if that autoclears it.

Thanks for all the input guys.