It could be as Bob suggests but it could be that your air filter is dirty and needs replacing. This would cause the engine to run too rich leaving unburnt fuel deposits on the lambda sensor in the exhaust system. When did you last check it and renew you air filter? If it is that, then after renewing it the unburnt hydrocarbons on the lambda sensors should burn off and the warning light should eventually go out.
ChicksFan
May 2013
Egr valve is dirty. Take it for a 30 minute run at high revs preferably on the motorway, alternatively take the valve out and clean it with the correct cleaner
Bob
April 2013
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