Depollution System Faulty

[colster]

car c4 Picasso year 2007 engine 1.6hdi problem for the last 3 years at least when the car has been driven on a longish journey the engine management light comes on with a warning depollution system faulty message as well, this will remain on for a few journeys then clear until it goes on another longish journey when it may happen again. car has done aprox 70000 miles and is driven on mainly short journeys say 5 miles. Any ideas to what the problem is  

[coastline taxis]

Could be one of many things. You can maybe start with changing one component at a time and spend a fortune trying to repllace the sensor (if it is a sensor at fault)  or you can get it plugged in and the scanner will tell you what area t0 look into

[paul.h]

When the engine management light comes on a fault code is stored on the ecu and stays there until it is erased by a code reader, even if the light goes out. The faut code will give a good indication of what the car thinks is wrong. If you do not have a code reader to find out what the fault is you can pay a garage to do this or buy one for less. One that gives some engine live data is more useful than a low cost one without, for example http://www.gendan.co.uk/product_FXNT200.html The actual fault could be anything that affects the exhaust emissions.

[arak81]

Buy a maxiscan like me, read the code and upload it here.. we will see which code it is and we can go from there.