I have P0133 error code (CEL). Bank 1 O2 sensor.
Where is it located on 1998 V70 ?
How do I replace it? From under the car or from the top?
Thanks!

There are probably some Youtube videos that show O2 sensor replacements. Your car has 2 sensors, before and after the cat.
The p0133 is for the front O2 sensor.

The plug for both sensors are on top of the transmission and close to the firewall. If you have a turbo, it will be difficult to see them. The grey plug is for the rear sensor.

Best bet, get under the car, passenger side and look up at the sensor. I had good luck with a 7/8" attachment designed for sensor removal.

This FCP video is a bit quick, just scroll down to seee the video box:
https://www.fcpeuro.com/products/volvo-oxygen-sensor-front-850-c70-s70-v70-15097
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My name is Klaus and I am a V♂lv♂holic

Thanks Klaus.
Do you know the correct part number for bank1 O2 sensor? There are many available. Some require extra cable extensions...some do not.
I just want to make sure I get the right one.

Turbo/non turbo? According to FCP fitment guide, just the early V70s needed the extension - they say 1997, which is not in the USA.
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My name is Klaus and I am a V♂lv♂holic

It's non turbo 1998 model. Plain vanilla FWD.

I suggest calling a Volvo parts department and asking them nicely for the part number and if the extra wire is needed. Keep your VIN handy, they might ask for the trailing numbers.
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My name is Klaus and I am a V♂lv♂holic