P0139 — O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)
Category: Powertrain Severity: Low
Updated:
DTC code P0139 means: O2 Sensor Circuit Slow Response (Bank 1 Sensor 2). It falls under the "Powertrain" category, with an estimated severity of Low. Common causes include aged downstream O2 sensor, exhaust leak and oil or antifreeze contamination; it's worth confirming the diagnosis before replacing parts.
Possible causes
- Aged downstream O2 sensor
- Exhaust leak
- Oil or antifreeze contamination
- Weak heater
Symptoms
- Check engine light
- No drivability symptoms
How to diagnose it step by step
- Check for exhaust leaks.
- Decelerate and see if the sensor drops quickly.
- Replace the sensor if it responds slowly.
How to fix it
It is usually a high-mileage downstream sensor. Fix any exhaust leaks before replacing it.
Estimated repair cost
$100–280.
Frequently asked questions
What does DTC code P0139 mean?
O2 Sensor Circuit Slow Response (Bank 1 Sensor 2).
Is code P0139 serious?
Severity Low. Usually a minor fault; check the causes listed.
Can I keep driving with code P0139?
Yes, it is safe to drive.
Related codes
P0138 P0137 P0136 P0135 P0134 P0133 P0132 P0140 P0131 P0141
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