Hi,

I've got a 2000 (W reg) Skoda Octavia 2L petrol with the engine 'check' light on. I took it to the local dealer, who diagosed a broken baffle in the cat, which may have confused the sensors. They reset the light. We then got the cat replaced, but the light came back on.

This time, we took it to an independent garage, who diagnosed a broken baffle in the back box (not the cat, after all!) and a faulty oxygen sensor. So we replaced both of those, and they reset the light.

130 miles later, and the light has come back on again. I'm fed up of this now - how hard is it to find and fix the *actual* cause of this light coming on? The garages seem to charge for an hour's labour just to read the fault codes out, so I'm reluctant to take it in again - is there anything I can check myself that might be the cause of this light coming on? The car generally runs fine, although a bit noisy when accelerating hard in low gears.

Finding the 'actual' cause is actually fairly difficult on the 2 litre engine. Many things can cause an emission based fault. Most common faults are either relating to a rich or weak mixture. Piston rings is a common issue meaning the engine breathes heavy and crankcase ventailation gets passed into the intake and picked up as a rich mixture.

Altitude correction can also be a fault, caused by either the air mass meter or on some 2000 MY cars a problem with the ECU programming.

Thanks for the ideas - can I check any of those myself, or do I need to keep throwing money at the garages until they get lucky? I've got the Haynes manual, but not with me right now...