P0139: O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)
Can you still drive? Yes, you can drive without concern. This code typically has no noticeable effect on drivability but will cause emissions test failure.
What Does P0139 Mean?
Code P0139 is set when the downstream oxygen sensor on Bank 1 responds too slowly to changes in exhaust composition. The ECU monitors how quickly this sensor reacts and flags this code when the response time exceeds acceptable limits. A slow sensor cannot accurately report catalytic converter efficiency.
Need to read your codes?
An OBD-II scanner lets you read and clear diagnostic trouble codes from your vehicle's computer. Most scanners work with any car made after 1996.
Browse OBD-II Scanners on AmazonCommon Causes
- Aging O2 sensor with degraded response time
- Contaminated sensor element
- Exhaust leak affecting sensor readings
- Failing catalytic converter affecting downstream readings
Symptoms
- Check engine light on
- Slightly reduced fuel economy
- Failed emissions test
- No noticeable drivability symptoms
Diagnostic Steps
- 1Read and document freeze frame data
- 2Monitor downstream O2 sensor response rate with a graphing scan tool
- 3Compare response time to manufacturer specifications
- 4Check for exhaust leaks near the sensor
- 5Inspect catalytic converter health
- 6Replace downstream O2 sensor if response is confirmed slow
Recommended Parts & Tools
oxygen sensor
O2 sensor socket
Estimated Repair Cost
| Type | Estimated Cost |
|---|---|
| Total Repair Cost Range | $50 - $300 |
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Chat with AI About P0139Commonly Affected Vehicles
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Frequently Asked Questions
What causes an O2 sensor to respond slowly?
Over time, the sensing element in an O2 sensor degrades from heat and exhaust byproducts. This degradation slows the sensor's ability to detect changes in oxygen levels.
Will P0139 affect my gas mileage?
Slightly. The downstream sensor has a minor influence on fuel trims, so you may see a small decrease in fuel economy, but it is usually not significant.
Community Fix Reports
Community reports are user-submitted and not verified by Auto AI Buddy. Results may vary.
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