P0159
O2 Sensor Circuit Slow Response Bank 2 Sensor 2
Oxygen sensor
Generic OBD-II
Medium
What it means
P0159 means the downstream oxygen sensor on bank 2 (sensor 2) is switching too slowly between rich and lean. As a rear sensor it mainly grades catalytic-converter performance rather than controlling fuel, so this rarely changes how the car drives. It's usually just an aging sensor, and it keeps the check-engine light on and can fail an emissions test.
Medium
Can I keep driving? Safe to drive — as a downstream sensor this barely affects driveability, but the light stays on and it can fail emissions.
Common symptoms
What you'll notice
- Check-engine light on
- Fails emissions or won't complete readiness monitors
- Slightly worse fuel economy
Common causes
Most likely first
- Aged or contaminated downstream O2 sensor (most common)Likely
- Exhaust leak near the sensor skewing its readingsCommon
- Damaged wiring or connector at the sensorCommon
- Sensor contamination from burning oil or coolantLess often
- Rarely, a failing ECMLess often
How to diagnose & fix
Work through it in order
- View the bank 2, sensor 2 switching speed in live data to confirm it's lazy.
- Inspect the exhaust for leaks upstream of the sensor.
- Check the sensor connector and wiring for damage or corrosion.
- Replace the downstream O2 sensor if it's simply aged out.
- Clear the code and re-test to confirm response speed recovers.
FAQ
Quick answers
Is it safe to drive with P0159?+
Yes. This rear sensor mainly grades the catalytic converter, so driveability is essentially unchanged. Fix it for emissions and to keep the light off.
Can I just clear P0159?+
It will return once the ECM re-tests the sensor unless the lazy sensor or an exhaust leak behind it is repaired.
Related codes
Often seen with P0159
Read & clear P0159 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX