Quick answer: The downstream oxygen sensor on Bank 2 is responding too slowly for trustworthy Bank 2 catalyst monitoring.
Drivers also search this fault as bank 2 sensor 2 slow response, rear O2 slow response bank 2, downstream oxygen sensor slow bank 2.
P0159 is the Bank 2 counterpart to P0139. It means the rear oxygen sensor on Bank 2 is changing too slowly, which can happen because the sensor is aging, contaminated, or being misled by exhaust conditions that keep the downstream signal lazy. In practice the code matters because it muddies Bank 2 converter conclusions far more than it changes how the car feels.
P0159 is usually not urgent, but it leaves Bank 2 catalyst monitoring and emissions readiness on shaky ground until the rear-sensor response issue is fixed.
Cause phrases often tied to this code: rear O2 sensor aging bank 2, contaminated downstream sensor, slow catalyst monitor witness, Bank 2 exhaust leak, lazy rear oxygen sensor bank 2.
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.
Yes. Both point to a slow downstream oxygen-sensor response, but on different banks.
Yes. A leak near the Bank 2 rear sensor can make the downstream signal react too slowly or inconsistently.
No. It proves the rear-sensor story is too slow to trust, which is different from proving the converter failed.