If you have engine fault light appear on the dash you can find out what triggered the fault by reading a code produced by the ECU.
You do this by performing THE KEY DANCE.......... Don't worry you don't need to put on you dancing shoes!!
Here is how its done
Turn your key until dash lights come on then switch back to ACC (not completely off )
Then again turn on again and back to ACC
Repeat a thrid time, then wait,
You will then see the fault codes codes displayed where your mileage was
The codes will be 4 digit codes starting with the letter P
Each fault code will be displayed for a few seconds and at the end the word "done" will come up
If there are no error codes it will just say "done"
If you miss the codes the first time, don't worry just do the dance again!
This ONLY works on the Petrol cars, it does NOT work on the CRD