P2096: Post-catalyst fuel correction reaches the lean limit

P2096 means that bank 1 post-catalyst feedback is requesting substantial enrichment in the reviewed GM fuel-control strategy. It describes the controller's correction authority, rather than directly identifying a failed oxygen sensor or catalytic converter.

Why positive correction produces a lean code

When the downstream oxygen signal appears lean, the controller increases its integral and proportional offsets to bias fuel control richer. In the displayed calibration, failure requires average integral authority of at least 80% together with average total authority of at least 40%. These are internal authority percentages; they should not be substituted for conventional short-term fuel-trim readings.

The controller samples at 100-millisecond intervals and evaluates an average over 50 seconds. An instantaneous lean voltage or a single fuel-trim snapshot therefore cannot reproduce the decision on its own.

Conditions that change the diagnosis

This monitor is enabled during cruise and acceleration, but not during idle or deceleration. A successful idle observation does not demonstrate that the diagnostic has passed in its operating window.

The source also accounts for excessive fuel vapor during purge because it can distort the result. With purge open, vapor at or above 18% for five seconds can suspend diagnosis; it resumes when purge closes or vapor falls to 14% or less for five seconds. Consider purge status when comparing two recordings.

The table documents a two-trip, Type B response. Confirm the applicable downstream-feedback strategy, its enable status and averaged correction after any repair. The code alone supplies no basis for choosing a sensor or catalyst replacement.

Source and applicability

This explanation is limited to the documented 2025 GM monitor; its thresholds are not universal vehicle specifications. GM diagnostic table, PDF page 588.