Engine warning light on C3 diesel

C3 SX diesel, bought December 2002.
About the middle of 2005, the engine warning light came on during a journey; I stopped and phoned the garage whence I bought the car.
I was told to wait a couple of minutes with the engine off; the system was being over-cautious. Good advice; that fixed it (and always has.)
However, it keeps happening, four times in one very unusual day during a journey of a little over 200 miles. Since mid December 2005, it's happened a total of nine times.
The garage seem puzzled; I was told to beware of driving too slow for the gear- go to gear n only at n*10 mph. They took details, saying that there had been other reports of this sort of problem. The exhaust recycling valve -have I got that right? -was mentioned after they connected it to their diagnostic kit..
Anybody else have a similar problem? The probability of my next car being a C3 was 90% a year ago; it's rather lower now. -- Per ardua ad nauseam

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.