O2 Sensor replacement (pre-catalytic, bank 1 sensor 1)

[mck159]

Hi all,

Hope you are doing well

O2 sensor in my 2009 Z4 E89 3.0i is broken and I need to replace it.

Fortunatelly it's one with easiest access - sensor 1 bank 1 (pre-catalytic-converter, one closer to front of the car, access from engine bay)

I'm a bit worried that when I do it something can go wrong, e.g. I can strip the thread, so wanted to ask about your experience, and also ask for some advice:

1. Did anyone of you do it, and was it hard to unscrew it, or it went easily? Did you need to use breaker bar?
2. Do you recommend doing it on hot or cold engine?
3. Do you recommend using wire brush and thread chaser to clean the thread before installing new sensor, or you would just screw in the new one?
4. Do I understand correctly that torque to screw it in should be 50Nm (I have torque wrench)?
5. Is there any reason to replace both pre-cat sensors if only single one is broken?

[colb]

Mt experience with changing post cat sensor on an E85 2.5 was difficult despite trying to use an O2 sensor removal socket, it just started to round off and wouldn't come out. In the end I had to chisel the top half off just leaving the Hex. Used a extractor socket on the rounded off Hex and with a short breaker bar managed to undo it and extract it. I used a thread chaser to clean the thread and refitted the replacement sensor.
https://www.ebay.co.uk/itm/126125876788 ... BM5tCth8xj

[flybobbie]

You could get exhaust hot then quench sensor with water just before unscrewing.