how can i fix the engine management light on my meriva?

My Vauxhall meriva 2005 has a car symbol with a spanner going through it showing on the dash every now and then - there is no pattern as to when it comes on.

the car has never lost power or has not exceeded on its fuel consumption -

I took it to a local garage and the computer has showed that there is a leak in a pipe coming from the exhaust???

Has anyone ever had a ny problems like this before i book the car into get the leak traced???