Normal lambda sensor behaviour?

I replaced my CAT for the MOT last month.



Since then on 3 separate occasions my EML came on.



Plugged in the ODB reader and it said the powertrain sensor on bank 1 was operating outside normal parameters.



Ran voltage check....came back as operating below expected result.



So I cleared the fault and thought nothing of it at the time, CAT was brand new and went on my way as the car performed fine.



Then it occured again. Same fault, although this time checks looked OK and no errors on the tests.



Then it happened yesterday. So whilst driving I got my GF to open Torque Pro and set the graphing to the 02 sensor on bank 1 voltage.



This is the result:







It seems to have periods on 0 voltage going to it. This is when the car was very warm and driving on a motorway at around 2.8-3K revs constantly.



This is the same circumstanecs that the error occurs every time - always on a motorway, always during long-period of motorway driving.



This morning on the way to work I pulled up the same graph and started plotting. This is the result:







Doesnt quite hit zero. The graph there would cover the engine from cold to warm, although oil temp didnt rise above 60 during this time.



Is this normal sensor behaviour or indication of a faulty one?

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