Anti-pollution light can have several causes:
Upstream or downstream oxygen sensors.
Coil pack.
Catalytic converter.
Fouled spark plugs.
Your best bet is to get a computer diagnostic done on the car and that will tell you what needs replacing.
Does the car misfire at all? If yes then check plugs and coil pack.
If it doesn't misfire but runs a bit lumpy and fuel economy is not so good any more then it is likely to be oxygen sensors.
Either way, don't leave it too long before fixing or you can end up choking up the catalytic converter.
The car can give an anti-pollution fault but still be running fine - the fuel trim that trips this fault is very sensitive and give the fault while it is still an intermittent fault in the early stages.
Don't let a dealer etc just reset the diagnostics and tell you it is fixed... the fault will come back again until you find the root cause.
Sean, October 2009
