P21D0: An injector B open-load code with an unresolved channel-to-cylinder mapping

The generic P21D0 designation is cylinder 2 injector B circuit/open. The cited GM row calls its monitored target injector 8. That is an unresolved mapping between generic cylinder numbering and the document's channel numbering; it does not by itself prove either naming scheme is incorrect.

What the electrical row establishes

The controller checks an inactive power stage and an output value at least 3 V but below 5 V for the open-load diagnosis. The source gives a three-event maturation count, with engine speed at least 80 rpm and supply voltage inside its stated 10.9–25.5 V window.

These conditions describe the diagnostic circuit's behavior. They are not a pin-level voltage instruction for whichever injector happens to be physically numbered two or eight on an engine.

Resolve identity before locating an interruption

The source's adjacent channel-8 rows provide separate low-circuit and high-circuit categories. Knowing whether the driver identified an open load rather than another electrical state is useful, but only after the vehicle's exact channel mapping has been established.

Retain the full code, controller identification and calibration information when selecting a circuit diagram. Do not move or replace a physical injector using the unresolved number alone. The monitor concerns electrical load recognition and does not establish fuel flow or a nozzle blockage. A successful retest must occur under valid monitor conditions; mere absence of a new code while the stage is ineligible is not evidence of continuity.

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 558 · GM PDF, physical page 559.