P2271

Code P2271 indicates that the downstream oxygen sensor on Bank 1 (Sensor 2, after the catalytic converter) is consistently reading rich or is biased toward a rich signal. This is the opposite of P2270 — instead of reading lean, the sensor is stuck high. Like its lean counterpart, this code typically doesn't cause noticeable drivability problems but will illuminate the Check Engine Light and cause an emissions test failure.

The downstream sensor monitors catalytic converter health by reading the exhaust composition after it has been processed by the converter. A properly functioning converter should produce a relatively stable, low-voltage signal from the downstream sensor. If the sensor reads consistently rich, it could mean the sensor itself is faulty, or the converter is not properly cleaning the exhaust gases.

Replace the downstream O2 sensor first, as it's the most common and least expensive fix. If the code returns, investigate whether the engine is running rich (check upstream fuel trims and other codes). A chronically rich engine can overload the catalytic converter with unburned fuel, causing the downstream sensor to read rich. Also look for oil consumption issues — blue smoke at startup or under acceleration suggests oil is getting past valve seals or piston rings and contaminating both the converter and the sensor.

Severity

Symptoms

• •Check Engine Light on
• •Slightly reduced fuel economy
• •May fail emissions inspection
• •Generally no noticeable drivability issues
• •Possible subtle sulfur or rotten egg smell from exhaust

Likely Causes

Estimated Cost

Common Fixes

1. Replace the Bank 1 downstream oxygen sensor (Sensor 2)
2. Inspect the catalytic converter for proper function
3. Address any upstream rich-running conditions that may be overwhelming the converter
4. Check and repair sensor wiring and ground connections

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