O2 Sensor Negative Current Control Circuit Low (Bank 2, Sensor 1)
What does P2251 mean?
The P2251 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Negative Current Control Circuit Low (Bank 2, Sensor 1). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Engine running lean on Bank 2
- Hesitation during acceleration
- Failed emissions test
- Rough idle
Probable Causes (Ranked by Likelihood)
- Failed wideband O2 sensor with low negative pump cell current Very High
- Short to ground in the negative current control wiring High
- Corroded connector reducing current flow Moderate
- Exhaust leak near the Bank 2 sensor Moderate
- ECM negative current driver outputting low Low
Step-by-Step Diagnostic Procedure
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Read Bank 2 Sensor 1 pump cell current data with a scan tool
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Check for shorts to ground in the negative current control wiring
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Inspect the sensor connector for corrosion or poor contact
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Check for exhaust leaks near the Bank 2 sensor location
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Replace the wideband O2 sensor if internal failure is confirmed
Frequently Asked Questions
What does low negative current mean?
Low negative current in the pump cell means the sensor cannot properly pump oxygen out of the measurement chamber, resulting in inaccurate lean-side air-fuel ratio readings.
Can I drive with P2251?
You can drive short distances, but the engine cannot properly manage the air-fuel ratio on Bank 2, which leads to poor performance and potential catalytic converter damage.
Is this a common failure?
Wideband sensor failures are not uncommon on higher-mileage vehicles. The pump cell degrades over time, and these codes become more frequent above 100,000 miles.