Can drive — fix at your convenience.
This code means the downstream oxygen sensor on Bank 1 (Sensor 2) is reporting a high voltage or responding too slowly, which the computer reads as a constant rich condition or a sensor that isn't switching as it should. It's most often caused by a worn or contaminated sensor, but wiring problems and connector issues can also be to blame. The usual fix is replacing the oxygen sensor or repairing its wiring.
$150 – $400
Varies by vehicle and root cause.
Usually yes, for the short term. Because this sensor handles emissions monitoring rather than engine control, the car should drive normally. Get it diagnosed within a week or two, and remember it will likely cause an emissions test failure until repaired.
Most repairs cost between $150 and $400. The oxygen sensor is the main expense, and labor is generally reasonable. If only wiring or a connector needs attention, you may pay less.
It's a low-severity code in most cases. The engine isn't in danger and you can drive in the near term, but it does affect emissions readings and may slightly worsen fuel economy. Fixing it promptly keeps it from masking a related fault.
Both involve the same downstream sensor on Bank 1, but P0139 is set for high voltage or slow response, while P0137 is set for low voltage. High voltage points more toward a rich reading or a lazy sensor, whereas low voltage suggests a lean reading. The diagnosis and likely fix often overlap, usually the same sensor.