P0139: O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)
MediumPowertrainO2 Sensors
What does P0139 mean?
P0139 is a diagnostic trouble code indicating "O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)". The ECU is detecting a voltage reading that is below the expected range in the o2 sensors circuit. This typically points to a wiring short, a faulty sensor, or a grounding issue.
Symptoms you may notice
- Check engine light (MIL) illuminated on dashboard
- Decreased fuel efficiency
- Rough or irregular idle
- Engine running rough
- Intermittent warning lights
Estimated repair cost
Typical range in Australia (parts + labour)
$200 – $500 AUD
Common causes
- Damaged or corroded wiring harness
- Loose or disconnected electrical connector
- Failed o2 sensors sensor or actuator
- Blown fuse in the related circuit
- Poor ground connection
What should you do?
This code sits in an engine peripheral, typically emissions or forced induction. It will not take braking or steering away, but it can put the car into limp mode, cost you fuel and fail a roadworthy. Book it in rather than clearing it and hoping.
Get a diagnosis for YOUR car
Code P0139 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.