Replacing Oxygen Sensors

[yema0003]

On my 2000 x5 4.4I, the Service Engine Soon Lights up intermittently!! The car still drives fine (nothing noticeable at least)!

After making an appt to take it to the dealer, the light goes out with no history of faults (did this to me twice ). . . When I told the technician this he told me if it stays on for more than two weeks to bring it in. And so far it hasn't.

I ran an OBD II scan on it and got the following two error codes:

P0135 O2 Sensor Heather Circuit Malfunction Bank 1 Sensor 1

P0170 Fuel Trim Malfunction

Has anyone experienced or dealt with this!!!

I have come to the conclusion it's caused by faulty oxygen sensors??

Does any one have any idea on how to replace the sensors, i believe there are four of them?

Thanks in advance!!!