P21DE: Interpreting injector B circuit low while the channel mapping is unresolved

P21DE's generic definition names cylinder 2 injector B circuit low. The GM source places this code in its injector-8 channel group. The pages do not explain the mapping from that document channel to physical cylinder numbering, so testing a guessed injector would be premature.

The electrical class is still identifiable

The row describes a short-to-ground category with output voltage above 5 V while the power stage is inactive. This is the source's internal diagnostic observation, not an instruction to expect that voltage at an unspecified external terminal.

A three-event count is listed, along with minimum engine speed and supply eligibility. Adjacent channel-8 entries use separate criteria for an open load and an active-stage high-current fault. Those distinctions can be preserved accurately even while physical identity remains unresolved.

What a useful diagnostic record contains

Retain the complete code, driver category, controller calibration and the command state. These details allow the applicable wiring information to identify the correct circuit before a component is judged.

The word “low” does not identify a fuel-pressure shortfall, and the monitor does not test injector spray or delivered quantity. Likewise, the reported electrical class does not isolate a particular wire, injector or internal output. Resolving channel identity and then following the vehicle's circuit procedure is necessary before a repair decision. Clearing the code without a completed eligible retest provides no confirmation that the original electrical condition has disappeared.

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.