Quick answer: The ECU sees little or no meaningful activity from the Bank 1 Sensor 3 oxygen sensor.
Drivers also search this fault as bank 1 sensor 3 no activity, rear-most O2 no activity bank 1, downstream oxygen sensor dead bank 1 sensor 3.
P0146 is the no-activity version of the Bank 1 Sensor 3 cluster. The rear-most monitored O2 signal on Bank 1 is flatlined, disconnected, or dead enough that the ECU cannot use it with confidence. That usually points to the sensor itself, the connector, or the wiring path rather than directly proving anything about converter condition. The important idea is that the monitor has lost a rear witness, not automatically that the catalyst failed.
P0146 is commonly driveable short-term, but rear catalyst monitoring and emissions readiness stay unreliable until the Bank 1 Sensor 3 activity returns.
Cause phrases often tied to this code: rear-most O2 flatline, dead downstream sensor, open circuit, unplugged connector, heat-damaged harness.
Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.
Useful when the driver knows the wording but not the exact DTC yet.
Often the ECU is seeing no meaningful activity, but the root cause can still be the sensor, the connector, or the wiring path.
Usually not by itself because it is a deep downstream monitor code, but it can block readiness and distort catalyst conclusions.
Yes. A dead rear-most sensor can make downstream catalyst monitoring unreliable, but it does not automatically prove the converter failed.