P0139
O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
The ECU detects that the downstream oxygen sensor on bank 1 reports an abnormally high voltage signal, suggesting a persistently rich exhaust condition past the catalyst, a shorted sensor, or wiring shorted to a voltage source.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Common causes
Ordered by how often each turns out to be the cause.
- Engine running rich (leaking injector, high fuel pressure)Common
- Sensor signal wire shorted to voltagePossible
- Downstream O2 sensor failedPossible
Parts involved
- Oxygen Sensor B1s2
- Oxygen Sensor Wiring
- Catalytic Converter Bank1
P0139 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.