Youe car has a particulate filter fitted in the exhaust and a resovior under the fuel tank. The filter needs changing at 50000 miles ( if its an early one) and the tank refilled. Then the ecu reset. Not a job i would advise doing yourself as the chemicals used are not nice and you will need a computer to reset it. Sometimes the ecu will need changing if the light stays on after its reset.
Matt
October 2007
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