Hopefully I can help..
What engine size and fuel type do you have?
How does the car perform since this fault?
In regards to the pulling is this under braking or acceleration for example.?
Whats its mileage and service history?
Hi..there thanks for getting back..
Ok the Anti-pollution fault warning or message is just basically a "generic emissions fault message" on these models can cover a fairly wide area of possible faults.and would generally make it impossible to give an exact or possible location of where your fault is without the proper diagnostics which this will need anyway as any garage would perform that first - especially as you mention since the car seems to be running ok without any noticeable performance issues since this has come up .not to uncommon for this to happen if these the case - it could be as a simple as a engine sensor out of parameter or fault which the ecu picks up on or either ignition,air intake, fuel injection related fault or problem/lambda,oxygen sensor "probably the most common", exhaust catalyst fault which an emission test may actually highlight too etc.....However the only real way you will know exactly why the warning has come on is to have the cars ECU fault memory accessed to retrieve the relevant fault code stored using a suitable diagnostic machine and this should give you/us/garage concerned a better idea where to start and check further. this primarily prevents any need to replace parts through guess work which would be the most expensive route and having these codes will make it allot easier to identify exactly where the fault is.so as above the best way forward would be the diagnostic path then take it from there based on whats found during the test..any good local garage or mobile tech with the equipment should be able to narrow this down for you you wouldn't really need to go near the dealer unless the fault is something more serious or needs a more in depth diagnostic.
In regards to the pulling issue first thing to check are the actual tyre pressures just to be sure they are both correct on the front.then next cause could be slight tracking/geometry alignment fault.the only real way to check that is to have the front wheel tracking checked.also check for obvious issues in regards to the lower control arms bushings and outer balljoint for any slight or excess movement any one of the three thing could cause the car to pull to one side or veering etc...I do hope this helps