Drive with caution — fix soon.
This code means the heater element inside the rear oxygen sensor on bank 2 isn't working correctly, so the sensor takes too long to reach operating temperature. The heater helps the sensor read accurately right after a cold start, which matters for emissions monitoring. It's usually fixed by replacing the oxygen sensor, though sometimes a blown fuse, corroded connector, or wiring fault is to blame.
$150 – $400
Varies by vehicle and root cause.
In most cases yes, since this code mainly affects emissions monitoring rather than how the engine runs. You may see slightly worse fuel economy, but it's safe to drive for short periods. Still, plan to have it repaired soon so it doesn't lead to other issues or a failed inspection.
Most repairs run between $150 and $400, depending on your vehicle and labor rates. The bulk of that is the oxygen sensor itself plus about an hour of labor. If the problem turns out to be just a fuse or connector, it can be considerably cheaper.
It's a low-to-moderate concern. The car remains drivable and there's no immediate safety risk, but ignoring it can hurt fuel economy and will keep you from passing emissions testing. It's worth fixing promptly but it isn't an emergency.
Modern oxygen sensors have a built-in heater so they can start reading accurately within seconds of a cold start. That heater element runs through many heat cycles and eventually wears out or develops an electrical fault, which is exactly what P0161 flags on this rear sensor.