Well, er... If the garage has told you that there was a fault code connected with the EGR valve (P4010 or perhaps, P4040), then the little yellow engine management fault light should have shown, at some time, if not now then in the past.

EGR fault codes can be intermittent. They can show up if, say, you have been stuck in heavy traffic and crawling along slowly. The engine gets hot and the EGR should open to cool down the combustion temperature. A coked-up valve will not pass quite enough gas and the sensor will spot this and bring up the engine management fault light. After a few days of normal driving, the fault light will go out, but the fault code will be stored and readable with a code-reader plugged into the diagnostic socket.

These days, it's my thoughts that you should have your own code-reader (mine cost £40 from a local parts shop) so that you don't get ripped-off.

Perhaps this lot are saying that the EGR valve is not working because there is a stored fault code for it? If it's not working and there's a fault code, then the engine management fault light should have been illuminated, surely?

The problem with the EGR valve on this engine is that it's down the back and has two water pipes from from the block connected to it's cooler, and so it's an expensive job to take it apart. Removing the valve involves a lot of top-end dismantling and draining the coolant, so you need new anti-freeze to refill when re-fitting it. In other words, don't take the EGR valve apart unless you're sure it needs it!