The best way to remove O2 sensors is with s special socket.

bmw o2 socket - Yahoo! Image Search Results

Something like this?
http://ts2.mm.bing.net/th?id=H.48524...51425&pid=15.1

What is the correct pre/post cat oxygen sensor socket for a 2002 525i? - Bimmerfest - BMW Forums

You can rent this tool from Autozone

What is the correct pre/post cat oxygen sensor socket for a 2002 525i? - Bimmerfest - BMW Forums

This is the BMW type socket.

There are other sources less expensive this is just for clarification.

Oxygen Sensor Socket - CTA 2065 - Free Shipping

P0134 Oxygen 02 Sensor Circuit No Activity Detected (Bank 1, Sensor 1).

Where exactly would this sensor be? Pre or post cat? side?

Thanks.

BTW, AutoZone sells Bosch O2 sensors that plug and play for $56.

you need to put your engine type in your signature. Assuming you have a 3.0, I believe that's the top front sensor.

:iagree:

Depend on the mileages, it might be time for both pre-cat O2 sensors. No need to replace the post-cat ones since they're there to monitor the cats performance only.

I am not completely devoted to one vendor but i would suggest checking Rockauto for O2 sensors and plugs. Genuine Bosch 13477 runs $44.79 as of yesterday and the Bosch 4417 E53 3.0 plugs are $3.77 each. Cheap, quick shipping too.