Hi Pete,

>>> I can see both sides of the argument.<<<

There is no argument, only a difference of opinion.

The operating range (voltage output) of a narrow band Lambda sensor is approx from 0.2 volts up to 0.8 volts, this is its FULL operating range.

The re-flash with regard to the P0420 code is a increase in the allowable differential amplitude between the Pre and Post sensors (during Decel)

Please note that it is an increase in the differential between the two and not a total exception to the reading.

The first post states that the post sensors are switching between 0.2 and 0.8 IE, their FULL range and as long as the sensor was up to temp (as well as the Cat) I read this as a failure of the OSC of the Cat.

I will quite happily be corrected and learn along the way, but we need the understand that the ECU will suspend OBD monitoring with the rear heater faults present, so we don't know how long the Cat has been under performing for.

Regards Mark