P0165: O2 Sensor Circuit Slow Response (Bank 2 Sensor 3)
The bank 2 sensor 3 oxygen sensor reacts too slowly.
Normal risk
Usually safe to drive. Have it checked soon.
Short answer · Can I keep driving with P0165?
Yes, usually. This sensor sits far down the exhaust and does not control the mixture, so the car drives normally. Have it checked soon so the emissions system can be monitored again.
What does P0165 mean?
Code P0165 means the engine control unit found that the signal changes more slowly than a working sensor does. An ageing or contaminated sensor, or an exhaust leak near it, are typical causes. Sensor 3 is a third oxygen sensor that only some cars have, usually after a second catalytic converter; it does not control the mixture.
What the car does when the code is set
The check engine light comes on. The engine still controls the mixture, but less precisely, so fuel economy may drop slightly and emissions rise. Most drivers notice no change in how the car drives.
How the system works
The front oxygen sensor measures the oxygen left in the exhaust after combustion. A narrowband sensor switches between about 0.1 volts (lean) and 0.9 volts (rich), and the engine keeps the mixture swinging around the ideal point. Wideband sensors give a continuous signal instead. The faster the sensor responds, the more precisely the engine can control the mixture. The engine control unit measures how long the sensor takes to switch, or to follow a deliberate change in mixture, and stores a code when the response is slower than its limit.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Aged oxygen sensorSensors slow down with age and contamination.
- Exhaust leak near the sensorOutside air distorts the reading.
- ContaminationOil, coolant or silicone residues coat the sensor tip.
- Wiring faultDamaged wiring or connector problems.
How it is diagnosed
- Check for related codesFix misfire, fuel-trim and heater codes first.
- Watch the sensor signalOn a warm engine at about 2,500 rpm, a narrowband front sensor should switch quickly between about 0.1 and 0.9 volts. Slow, lazy switching confirms the code.
- Inspect for leaks and contaminationLook for exhaust leaks and inspect the sensor tip for white, black or oily deposits.
- Replace with the correct sensorUse the sensor type specified for your engine and clear the code afterwards.
Questions about P0165
Where is sensor 3?
It is the third oxygen sensor along the exhaust, counted from the engine. Bank 2 is the side of the engine without cylinder 1; the service data shows its exact position.
Can a lazy oxygen sensor cause a catalyst code?
Yes. A slow front sensor degrades mixture control, and the test of the converter can then fail. Fixing the sensor first saves money.
How long do oxygen sensors last?
Many manufacturers specify no fixed interval, but sensors often slow down after about 150,000 km. Contamination shortens their life.