What it means
The ECU detects abnormally high voltage from the third O2 sensor on bank 2. Indicates rich exhaust or wiring shorted to voltage.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 2 Sensor 3 is the third oxygen sensor in the bank 2 exhaust path on vehicles equipped with it. P0165 sets when the ECU sees a signal voltage that is too high, which can indicate rich exhaust or a signal wire shorted to voltage.
Common causes
Most likely first.
- Rich exhaust condition
- Signal wire shorted to voltage
- Connector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Use freeze-frame and live data to confirm that Bank 2 Sensor 3 stays unusually high when the code sets.
- Inspect the sensor connector and harness for corrosion, damaged pins, melted insulation, or a signal wire contacting a voltage source.
- Check for engine conditions that can make bank 2 exhaust genuinely rich, using fuel-trim and related live data.
- Test the signal circuit for shorts and check sensor power and ground against the manufacturer's specification.
- If the circuit is sound and rich running is not indicated, test Bank 2 Sensor 3 before replacing it.
Common fixes
- Repair a poor or corroded Bank 2 Sensor 3 connector.
- Repair a signal wire shorted to voltage or damaged by exhaust heat.
- Correct a confirmed engine condition causing rich exhaust.
- Replace Bank 2 Sensor 3 if its signal remains high with a sound circuit and normal exhaust mixture.
Can I keep driving?
The vehicle may remain driveable, but a genuinely rich condition can waste fuel and harm the catalytic converter over time. Avoid hard driving and address it promptly if there is a strong fuel smell, smoke, or rough running.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.