What usually causes it
- An old, worn out oxygen sensor
- An exhaust leak near the sensor
- Oil or coolant residue on the sensor
- Damaged wiring or a loose plug
P0139Starts at: OK to drive, fix when convenient
Oxygen sensor is slow to react (bank 1, sensor 2)
The oxygen sensor checks the exhaust. Sensor 2 sits after the catalytic converter (the exhaust part that cleans the fumes) on the side of the engine with cylinder 1, and it reacts too slowly.
Check this first
Listen for ticking or hissing from the exhaust, which points to a leak.
What to watch for
- A rotten egg smell from the exhaust
- Poor gas mileage
- A flashing check engine light, which means a bad misfire
Can I keep driving?
We rate P0139 as OK to drive, fix when convenient, as a starting point. Keep an eye on the signs below. If the light starts flashing, stop driving soon.
Quick answers about P0139
What does P0139 mean?
Oxygen sensor is slow to react (bank 1, sensor 2). The oxygen sensor checks the exhaust. Sensor 2 sits after the catalytic converter (the exhaust part that cleans the fumes) on the side of the engine with cylinder 1, and it reacts too slowly.
Can I keep driving with P0139?
We rate P0139 as OK to drive, fix when convenient, as a starting point. Keep an eye on the signs below. If the light starts flashing, stop driving soon.
What usually causes P0139?
The most common causes, in order: An old, worn out oxygen sensor; An exhaust leak near the sensor; Oil or coolant residue on the sensor; Damaged wiring or a loose plug.
Estimates only. A mechanic should confirm. The same code can mean slightly different things on different cars; the app explains it for your exact year, make, model and mileage.