Downstream O2 sensor flat-lines @ 0V
 

I've been restoring my '00 Disco 2 and run into a weird issue: downstream O2 sensor flatlines at 0v after the engine gets warm. It does work fine if I'm driving slow in city traffic, but once I rev it over 2000 RPM it just goes lean and spits 0V (and stays that way until the engine is fully cooled down). Upstream sensor is working fine and the engine runs smooth. Not sure if this is an issue with the CAT, exhaust leak somewhere, or whatever else it could be.

I have a spare brand new sensor which I used to check if the old one went bad, but it does exactly the same thing. Once removed from exhaust they seem a bit too sooty.

Just as a side note: I've rebuilt the engine top end - all new seals and gaskets. It also has new coils and sparks plugs. No misfires. No vacuum leaks.

Any thoughts?

Thank you for any help!

Miron

Found this video: looks like exactly my problem

Problem solved
 

To answer my own question, I got a bottle of cataclean and run it through the system - problem gone. Time to replace the cat