P2271: Rear oxygen sensor remains rich during the fuel-cutoff test

P2271 means bank 1 sensor 2 did not reach the expected lean voltage during the reviewed GM intrusive fuel-cutoff test. It is the fourth monitor in a six-test downstream-sensor sequence, following earlier checks that help establish whether its result is meaningful.

Read the threshold as a response test

With fuel cutoff commanded, the controller accumulates airflow mass and observes the rear oxygen signal. Failure is defined by voltage remaining above 100 mV after more than 30 grams of air have accumulated in the test.

The threshold is not a universal statement that any voltage above 100 mV indicates a rich fault. Its meaning depends on the deliberately lean test condition and the permitted accumulated airflow. Air mass is also not the same quantity as instantaneous airflow rate.

Sequence and prerequisites affect completion

The source excludes several preceding downstream-sensor faults, including P2270, as well as relevant temperature, airflow, fuel-trim, injector and misfire fault groups. Learned heater resistance must be valid and supply voltage must exceed 10.5 V. An inhibited test cannot supply a passing result.

Normally the diagnostic runs once per trip, with fast-response exceptions, and it has Type B, two-trip behavior. Preserve whether the commanded cutoff and airflow opportunity actually occurred when evaluating an intermittent complaint.

Verification should show the expected lean transition within an eligible test. The table establishes an insufficient sensor response, not a conclusive failed sensor, leaking injector or catalyst diagnosis. Those distinctions require additional service evidence.

Source and applicability

Use these facts only after confirming the documented system and calibration for the vehicle. GM diagnostic table, PDF page 631.