How do i find where an exhust leak is coming

P1351 VVT Sensor Range/Performance Problem (Bank 2)

run the fault codes to ensure that the EGR valve is faulty. Engine lights to not always come on unless there is something drastic going on with the engine /gearbox so that you can stop the car before damage is done.

if you only drive your car on short journeys the exaust system carbons up and you give out more emissions .the mechanic is right drive it a long distance ,and bring it back in while it is really hot to be ytested

There should be a 10amp fuse in the fuse box for the instrument panel that powers the light. The light is grounded by the computer.
Have you checked the fuses in the passenger compartment ?

Whenthe check engine light comes on, one or more diagnostic trouble codes (DTC) are stored inthe engine control module.
super vag k can plus can help you clear the fault codes.

The gas may be old I would put some Lucas in the tank and run it good.

Have a code test done (most larger parts stores do that free) In some cases you may need a shop to put a scanner on it to find specific out of range sensors that may not yet be bad enough to set a code.
I'd also check all vacuum lines and line connections as a small leak can alter the system readings. All the sensors on your car work together and the computer reacts to all the information it receives... Bad info in, bad info out...Only good testing will find the problem.
Primary sensors to pay attention to are the coolant temp sender, MAP sensor, throttle position sensor, manifold air temp sender, mass air flow sensor (if you have one) and the egr valve.and pcv valve (if you have them)
Good testing involves using a digital multi-meter and using instructions for that in chilton or haynes manuals. Replacing parts without testing can get really expensive. (but you have already found that out)
Good luck!

one end goes to intake manifold vacuum nipple and the other one goes to the evap [carbon] canister

REPLACE OXIGEN SENSOR AND CHECK GAS RECIRCULATED VALVE AND VACUUM LINES