Given the number of sensors and actuators on a modern car there are too many possibilities. The only practical solution is to get the car plugged in to a diagnostics computer.
Unfortunately Vauxhall diesels do not communicate well with every type of diagnostics computer, so you may have to go to a Vauxhall dealer or specialist who has the "TECH-2" system.
If you use other systems they may not connect to the cars onboard computer, then the tester/technician will try to tell you your onboard computer (ECM or ECU) is faulty and offer to sell you a new one for a horrendous price.
I signed up with a Vauxhall owners club (www.vvoc.com) and one of the members plugged my car into his Op-Com diagnostic for a case of beer, so worth a try!
Once you have the fault codes either post them in a new question on here , or I'll see you over on VVOC!!
vectracdti, February 2011
