Oxygen sensor slow response (Bank 1 Sensor 2)
The specified oxygen sensor signal changes too slowly during the vehicle's response monitor. A slow response is different from a completely open circuit. Heater operation, fuel mixture and exhaust integrity need checking before attributing the delay to the sensor itself. Bank 1 is the cylinder 1 side; sensor 2 is after the catalytic converter.
Can I keep driving?
If the light is steady and the vehicle behaves normally, contact a shop for vehicle-specific urgency advice. If there is severe shaking, stalling, major power loss, a flashing light, smoke or a fuel smell, pull over safely and arrange assistance.
What does this code mean for your car?
The same code can need different checks depending on the model and engine. Enter your vehicle details to find relevant sources and checks.
Symptoms
- Check engine light, possibly without noticeable driving symptoms
- Sensor reading that does not respond as expected during professional testing
- Incomplete emissions readiness or an emissions inspection failure
Possible causes
- 1Signal wiring or connector damaged by heat or chafing
- 2Failed or contaminated oxygen sensor
- 3Exhaust leak near the sensor affecting measurement
- 4Abnormal fuel mixture or sensor heater trouble affecting response
These possibilities are not ranked by frequency and do not diagnose your vehicle.
Checks you can safely do yourself
Safe checks only: engine off and cold, car on level ground.
- Save all codes and any freeze-frame data your scanner displays before clearing or repairs.
- Note accompanying fuel-trim, misfire or sensor-heater codes. Do not touch sensors or wiring on a hot exhaust system or crawl under the vehicle.
When you need a shop
Identify Bank 1 Sensor 2 from the vehicle exhaust diagram. Have the shop test signal and wiring, heater operation, exhaust sealing and fuel trims. Response testing must match sensor technology; a wideband sensor does not use the same signal pattern as a narrowband sensor.
How much does it cost?
A US repair estimate needs a diagnosis and a local shop quote.
We do not have a verified US repair quote for this fault. Request 2-3 itemized estimates after diagnosis; vehicle, parts and labor determine the cost.
Get 2-3 quotes
Investigate this code for my carFAQ
Can I keep driving with P0139?
If the light is steady and the vehicle behaves normally, contact a shop for vehicle-specific urgency advice. If there is severe shaking, stalling, major power loss, a flashing light, smoke or a fuel smell, pull over safely and arrange assistance.
What can cause this code?
Possibilities include signal wiring or connector damaged by heat or chafing; failed or contaminated oxygen sensor; exhaust leak near the sensor affecting measurement; abnormal fuel mixture or sensor heater trouble affecting response. The code does not rank causes or identify a part that must be replaced.
Does clearing the code fix the fault?
No. Clearing the code does not repair its cause or prove the fault is absent. It can erase diagnostic data and reset readiness monitors. Even if the code does not reappear immediately, the repair needs verification using the tests appropriate to the vehicle.
What if this code appears during a pre-purchase check?
Arrange an independent professional inspection before buying, including stored data, readiness status and written diagnostic findings. Identify Bank 1 Sensor 2 from the vehicle exhaust diagram. Have the shop test signal and wiring, heater operation, exhaust sealing and fuel trims. Response testing must match sensor technology; a wideband sensor does not use the same signal pattern as a narrowband sensor.
How much does repairing P0139 cost?
We do not have a verified US repair quote for this fault. Request 2-3 itemized estimates after diagnosis; vehicle, parts and labor determine the cost.