P2179: Interpreting bank 2’s excessive off-idle fuel adaptation

P2179 is the bank 2 lean off-idle code. The GM source links it to the multiplicative portion of long-term fuel trim in gasoline mode exceeding a calibrated limit. The affected bank and adaptation component are central to interpreting the result.

The monitored quantity is a factor

The row gives a threshold above 1.27 for bank 2. Its short evaluation period applies only with multiplicative adaptation active and the integrator stability or similar-condition requirements fulfilled. The continuation evaluates speed, load and changes in the learned factor.

A bank 1 value cannot stand in for bank 2's result, and a short-term correction is not the same quantity as the learned multiplicative factor. Confirm which parameter the scan tool is showing before treating its number as the monitor input.

What makes a comparison useful

Comparing the two banks under matching operating conditions may help frame an investigation, but this code alone does not establish whether the underlying cause is shared or confined to bank 2. The table reports the adaptation outcome; it does not isolate an air path, fuel component or sensor.

Retain bank 2's factor, adaptation activity, stability and load at the event. A temporary return toward normal while conditions change does not establish a completed pass. The applicable calibration's learning and diagnostic eligibility must be satisfied again. These distinctions make the code useful as evidence of excessive correction without turning it into an unsupported automatic parts recommendation.

Source and scope

2025 GM 25OBDG07A Part 2 monitor tables only; model, engine and transmission applicability are not established by the unresolved application-matrix filename join. These are documented monitor criteria, not a universal repair procedure. GM PDF, physical page 187 · GM PDF, physical page 188.