P0139 — O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
Can drive — fix at your convenience.
What P0139 means
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.
Common symptoms
- Check engine light is on
- Slightly reduced fuel economy
- Failed emissions or smog test
- Normal driving with no obvious power loss
- Possible faint fuel smell from the exhaust
Common causes
- Aging or contaminated downstream oxygen sensor
- Damaged or chafed sensor wiring
- Corroded or loose connector
- Internal sensor short causing high voltage
- Less often, a rich-running engine condition
Typical repair cost
$150 – $400
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0139 code?
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.
How much does it cost to fix a P0139 code?
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.
Is a P0139 code serious?
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.
What's the difference between P0139 and P0137?
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.