P0139 Code: O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)
🟢 Low severity · drivable
Safe to drive — this downstream sensor fault mainly affects emissions monitoring.
What P0139 means
The bank 1 downstream oxygen sensor is responding too slowly to changes in the exhaust. It's usually a sign the sensor is aging or contaminated.
Symptoms
- Check engine light is on
- Usually no driving symptoms
Common causes
- most common: Aging or contaminated downstream oxygen sensor
- common: Exhaust leak near the sensor
- less common: Oil or coolant contamination of the sensor
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Replace the bank 1 downstream oxygen sensor | Yes | $60–200 |
| Repair an exhaust leak near the sensor | Mechanic | $50–200 |
Frequently asked questions
Can I drive with a P0139 code?
Yes. It mainly affects emissions monitoring, not drivability.
What is the most common cause of P0139?
An aging downstream oxygen sensor.
How much does it cost to fix a P0139?
Typically $60–$200 for a new downstream oxygen sensor.
Related codes
P0136
P0136 Code: O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)
P0133P0133 Code: O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
P0420P0420 Code: Catalyst System Efficiency Below Threshold (Bank 1)
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.