2001 Zafira 1.8 Emissions Light?

At end of 2009 my emissions light and skid light came on at the same time and stayed on. RAC guy said it could be coil. Vauxhall garage had my car for 3 weeks in all! Told me it was main computer and after failed 1st parts order eventually got new part - ECU. Then it was fine. Today 16 months later exactly the same has happened. Garage seeing it next week. Any ideas and how safe to still drive. It was happy throughout all the freezing cold and snow, any chance something is leaking or cracked somewhere, it has been a bit sluggish on gear change.