P219F: do not infer a cylinder-four part failure from the imbalance code

P219F identifies cylinder-four air-fuel imbalance in the generic code mapping. The cited GM monitor places it in a shared family that compares each cylinder's calculated mixture behavior with its bank average. The source gives a detection method, but not a component-specific verdict.

A cylinder address is not a cause

The fourth cylinder must be located using the actual engine's numbering convention. The document does not establish that numbering or assign this code to every model listed elsewhere in the parameter file. An injector, ignition component or mechanical condition should be investigated only through the matching diagnostic procedure and the recorded evidence.

Both lean and rich branches can produce P219F. Consequently, the first useful distinction is which side of the bank-relative comparison failed. A repair explanation that assumes “not enough fuel” solely from the code has skipped that distinction.

The monitor has a defined opportunity to run

GM requires valid roughness information, plausible segment timing and completed synchronization. Active rough-road detection disables the relevant comparison, and speed and relative air charge must lie in a calibrated region. Those prerequisites should be considered when interpreting a recent test or an apparent lack of recurrence.

The table lists a once-per-driving-cycle evaluation and a two-trip classification. Clearing memory then watching a stationary engine is not equivalent to demonstrating a completed passing monitor. Preserve the original operating data, investigate the confirmed direction and verify cylinder-four behavior during a suitable, safely obtained monitoring opportunity.

Source and applicability

GM 2020 20OBDG07 shared cylinder air-fuel imbalance monitor. Only the cited monitor and calibration are described; per-code vehicle and engine applicability has not been established.

20OBDG07 Diagnostics, physical PDF pages 129, 130, 131, 132, 133, 134.