Octavia 2004 TDI 66kw engine has engine light on had it checked at dealers they found no faults only stored codes 18027 17946 17849 19561 17957 they reset code next day same again had it checked they found no faults only codes this is happening every two to three days help .could there be a faulty cable or solenoid have checked out solenoid they are giving resistance of 15 ohms and there is voltage 12 volts to them when ignition is on .

Change dealer for someone actually competent. The fact that there are fault codes being raised means that there is something wrong. I've no idea what from just the numbers though, and can't even guarantee that the Rosstech wiki will help since we don't know what code reader was used.

Dealer has test all conponent and they said all is ok found cpu faulty and need to replace it £1100

CPU faults do occur, but are rare. Some main dealers have a bit of a tendancy to "assume the worst" if they don't get data that says "replace the gasjit on the firmaset" though.