hi all, new to this site and would appreciate some help, i have a 04 plate 520i with the engine management light on, when scanned it gave these two error codes:
2717 oxygen sensor pre cat bank 2 error
29A3 oxygen sensor pre cat bank 2 signal
scanner was a snap on solus i believe

after going to my trusty garage who ive used with all my previous bmws, i purchased a new lambda sensor (nfk brand) pre cat for bank 2 (4-6 valves), the sensor was fitted and codes reset, drove home no warning lights . happy. next morning starts car drives 20 yards and up pops the engine light again! not happy. took it back to the garage and re scanned and showed the same codes. the car was checked for air leaks none found. the scanner showed through the scroll files ( not sure of the technical terms) the sensor control is not active. what is the cause of this? what part needs to be replaced? any info would be gratefully accepted.