Please Help P0139 code
 

I recieved the following code P1039 on my BMW X5... does anyone know what this code means, I believe it is an O2 sensor, which one? front of the cat or behind the cat? how difficult are these to change?

Thanks

from Bentley manual, o2 sensor circuit slow response bank 1 sensor 2. unless of course u meant P1039. luckily the same for all engines. let us know your details next time in case it matters...

Thanks
 

Does this code mean the O2 sensor behind the Cat?

To tell you exactly where - we'd need to know what engine you have. On the I6 3.0L, there are 4 O2 sensors. 2 before the cat, 2 after. If this code were to be applied to the I6, you'd be troubleshooting the O2 sensor closest to the front of the vehicle, after the cat.

are you saying retro to the exhaust flow?

how can it be both closest to the front of the vehicle and after the cat?

why would the 4.4 not have 2 before and 2 after as well??

First off, it is code P0139, not P1039 right?

If it is P0139 than the post cat 02 sensor is reading/responding slow. This doesn't affect how she drives, just monitors the emissions after the catalyst. If you have the I6 (3.0i) then it is the sensor after the cat converter for the front manifold, which you get to from underneath the vehicle. If you have the V8, then it is the one after the cat converter on the passengers side, still get to it from underneath.