The engine warning light comes on

Hi everyone
I have an S type Jaguar 4.2 V8 2004 model 77000 driven

Once every month since the last 3 months the engine fault light comes on and it displays reduced performance on the dashboard

i take it to Jaguar dealer and they run the fault codes and charge 63 pounds each time and its a fuse or the light fault
is there a cheaper way to know whats wrong or why the engine fault light comes on?

thanks