Summary
P0161 means the heater circuit in the downstream O2 sensor on Bank 2 has failed. This is the Bank 2 post-catalytic-converter sensor, used to monitor converter efficiency. The most common cause is a burned-out heater element (60%), followed by wiring or connector damage (20%) and a blown fuse (15%). This sensor doesn't control fuel delivery, so the impact is limited to delayed catalyst monitoring and a failed emissions test.
Severity: Low
Safe to drive: Yes
Repair cost: $20–$200 depending on cause
DIY difficulty: Easy to Moderate
What does P0161 mean?
The Bank 2 downstream (post-cat) O2 sensor monitors catalytic converter efficiency on Bank 2. Its internal heater brings it to operating temperature quickly after engine start. P0161 sets when the PCM detects the heater isn't drawing the expected current — usually an open circuit from a burned-out element.
This sensor only monitors the converter — it doesn't directly control fuel delivery. A heater failure delays the catalyst monitor but doesn't affect how the engine runs.