2015 Mustang 5.0 high voltage downstream O2 sensors

First off not sure if someone used a handheld tuner (never used one) to disable the downstream sensors because the I/M readiness shows the sensors but they are constantly incomplete. He has several hundred miles on it but still incomplete. (May have heater circuit INC also)

He just bought the car (auction), looks like it has aftermarket headers and aftermarket cats. The upstream sensors appear to be cross counting normally (.2-.8 volt range). The downstream sensors do show constant HIGH voltage from .9 to over 1 volt.

If the downstream sensors were turned off with a programmer, they would show INC for the I/M readiness, but will they still data stream?

Any suggestions

Thanks

Just unplugged both downstream O2 sensors and with car running no MIL and the values remain .9+ so it looks like the pcm has the sensors programmed out.