P21D2: Open-load evidence for injector B without assuming the source’s channel number

P21D2 is listed generically as cylinder 4 injector B circuit/open. The GM table labels its corresponding row injector 2. This article keeps those identities separate because the source pages do not establish how that internal channel maps to physical cylinder numbering.

The documented open-load mechanism

The monitor evaluates output voltage with the power stage inactive. Its open-load window is at least 3 V and below 5 V, with three diagnostic events required. Eligibility includes engine speed of at least 80 rpm and battery voltage above 10.9 V but below 25.5 V, plus referenced inhibition conditions.

These criteria explain how the controller classifies the electrical state. They do not establish that an external injector terminal should read the same voltage under an arbitrary meter test.

Preserve the distinction from neighboring failures

The same document channel has separate low and high electrical codes. An open-load result is therefore more specific than a broad injector-performance complaint, but it still does not identify where the interruption occurs.

First resolve the channel-to-cylinder mapping from the exact engine and controller information. A physical-cylinder assumption would risk testing the wrong circuit despite correctly understanding the monitor. Then use the appropriate circuit procedure to distinguish wiring, load and driver behavior. No fuel-flow or spray-quality measurement is part of this row, so a mechanical injector replacement cannot be justified from the open-load code alone.

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 555 · GM PDF, physical page 556.