P0139
Low SeverityO2 Sensor Circuit Slow Response (Bank 1, Sensor 2)
Emissions System
What Does P0139 Mean?
The downstream O2 sensor on bank 1 responds too slowly. This can mask catalytic converter degradation.
Common Fix
Replace downstream O2 sensor
Estimated Cost (DIY)
$25 - $80
Common Causes
How to Diagnose P0139
- 1Monitor sensor response rate
- 2Check for oil consumption
- 3Replace sensor
OEM Diagnostic Flowchart
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Related Resources
Repair guides, symptom pages, and wiring diagrams related to P0139.
OEM Manual Evidence
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Related Symptoms
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Exact Repair Workflows
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Related Codes
General fault with the downstream (post-cat) O2 sensor on bank 1. This sensor monitors catalytic converter efficiency.
The downstream O2 sensor on bank 1 shows no voltage changes at all. The sensor is likely dead.
The catalytic converter on bank 1 is not converting pollutants efficiently. This is one of the most common DTCs.
Frequently Asked Questions
- Does P0139 mean my cat is bad?
- No, P0139 is specifically the sensor responding slowly. Replace the sensor first before worrying about the cat.
- How often should downstream O2 sensors be replaced?
- Typically every 80,000-120,000 miles, or when codes appear.
Related Repair Guides
If your vehicle has triggered P0139, these DIY repair guides may help: