What does code P0139 mean?
The rear oxygen sensor responds slowly and does not track mixture changes promptly
OBD-II Code
P0139 — Oxygen Sensor Circuit Slow Response Bank 1 Sensor 2
The rear oxygen sensor responds slowly and does not track mixture changes promptly
Common symptoms
- Slight increase in fuel consumption
- check engine light
Possible causes
- Aged oxygen sensor
- sensor contamination
- small exhaust leaks
Initial recommendation
Replace slow responding sensor and inspect exhaust leaks.
Safety notice
This information is for guidance only and does not replace a physical vehicle inspection or diagnosis by a qualified mechanic. If the vehicle has severe power loss, smoke, a fuel odor, overheating, brake or steering problems, or any unsafe behavior, avoid driving it and seek professional inspection.
Analyze this code with MecaOBD
Use the app to combine code P0139 with your vehicle's actual symptoms for more complete diagnostic guidance.
Go to the app View more codes