I had a coil go, RAC came out and replaced it. Got home and the next time I started the car the light was back on but no symptoms, error code was the same coil they replaced so had it reset.
Sure enough next time I started the car it was back on again.
Had the RAC out again today, they changed the same coil and so far no light. The patrolman reckoned that as they don't use genuine Seat parts that the resistance in some of the coils falls outside the usual range and the ECU doesn't like it so throws its dummy out.
Thankfully though because the coil was faulty RAC fixed it for free.