You do not say what engine or year your Cav is but i would guess it has a eurotec engine in.
There could be a number of problems but the common fault with this engine is oil from the rocker getting around the plugs. This shorts out the spark and then the engine management light will come on. Another favorite would be the cam belt sensor causing a problem. Again the light would come on and you probably find it hard to start the engine.
Get yourself onto an owners site like VX owners. You will find lots of information there and probably the right answer.
DaveL
February 2007