O2 sensor heater circuit (B2S2)
What P0161 means
Your car's computer set P0161: O2 sensor heater circuit (B2S2). It belongs to the fuel and air metering group of codes. It is a generic code, so it means the same thing on every make. The check engine light usually comes on once the fault has been seen on two drives in a row. Until then it shows up as a pending code.
Can I keep driving? Usually safe to drive. The car may run normally, but it will not pass an emissions test until this is fixed.
Common causes
- Failed heater element inside the oxygen sensor
- Blown fuse for the O2 sensor heater
- Damaged wiring or connector (often near the hot exhaust)
Fix the cheapest, most likely cause first. Clearing the code without a repair only turns the light off until the fault comes back.
Check it yourself
The heater only matters while the engine warms up. Check the fuse first, then the sensor connector.
Torque Deck reads P0161 with a cheap Bluetooth OBD2 adapter. It also shows the freeze frame (engine conditions at the moment the code set) and the live data you need to narrow it down.
Parts
Parts most often replaced for P0161: downstream oxygen sensor. Confirm the cause first, and match the part to your exact engine.
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Related codes
This page explains what the code usually means. It is not a diagnosis of your car. When in doubt, ask a mechanic.