OBD-II Code · Sensors
P0139
O2 Sensor Slow Response (B1S2)
low severitySafe to drive$150-$400
Downstream sensor slow to respond.
Common symptoms
- CEL
Likely causes
- Aging sensor
- Contamination
Where to start
- Try the cheapest cause first. Start by checking: aging sensor.
- Cost & scope. $150-$400
- If the code returns after the fix: escalate to a shop or scanner with live-data and freeze-frame. A code that re-sets means the underlying fault is still there.
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