P2271 moderate

O2 Sensor Signal Stuck Rich (Bank 1, Sensor 2)

What does P2271 mean?

The P2271 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Signal Stuck Rich (Bank 1, Sensor 2). This is a moderate severity code.

Common Symptoms

  • Check Engine Light on
  • Catalyst efficiency code may also appear
  • No drivability impact

Probable Causes (Ranked by Likelihood)

  • Failed downstream O2 sensor stuck at high voltage Very High
  • Catalytic converter passing excess fuel (poor efficiency) Moderate
  • Wiring fault shorting downstream sensor signal high Low

Step-by-Step Diagnostic Procedure

  1. Monitor downstream sensor voltage. Stuck above 0.7V under steady cruise indicates sensor failure or cat passing excess fuel.

  2. Compare to upstream sensor behavior. If upstream is normal, focus on downstream sensor and cat.

  3. Replace downstream sensor and retest before condemning the catalytic converter.

Frequently Asked Questions

Should I replace the downstream O2 sensor before the catalytic converter?

Always yes. The downstream O2 sensor is far less expensive ($50-$200) than a catalytic converter ($350-$2,500). A stuck sensor is more likely than a failed cat on vehicles under 150,000 miles. Replace the sensor first and retest.

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