UK P1115 Code and Pre-Cat O2 Sensor Help

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Hi,

I have a UK Boxster S 986 2001. I have the CEL light on and the diagnostics say it’s code P1115, pre cat O2 sensor.

I have a couple of questions-

• How easy is this to change, I’m not to cleaver with a spanner?
• Is there a guide on-line that I can follow?
• Are the pre and post cat sensors the same?
• Of the two sensors on this page what one do I need-http://www.eurocarparts.com/ecp/k/o2/p/Car-Parts

Thanks guys!