P21D4: The cylinder 6 injector B open-load test uses an inactive output

P21D4 is the generic cylinder 6 injector B circuit/open code. The GM source identifies injector channel 6 and describes an off-state electrical load check. Its criteria concern what the driver sees electrically, rather than how much fuel the injector delivers.

The open-load window is not an energized-current test

The output must fall in the documented interval from 3 V inclusive to below 5 V while the power stage is inactive. The source lists three events, engine speed at least 80 rpm and a battery-voltage operating window above 10.9 V and below 25.5 V.

An energized injector-current observation answers a different question. The neighboring high-circuit category is evaluated with the stage active, so substituting that operating state would not recreate the P21D4 check.

Interpreting a retest

The table references further inhibition conditions. A period without a new fault only provides meaningful evidence if the open-load monitor was eligible and actually ran. An output that remained disabled for another reason is not automatically a passed load test.

Confirm the exact engine's injector B configuration and circuit identity before locating an interruption. Matching channel and generic cylinder numbers do not supply a connector location or establish universal applicability. The code cannot distinguish an interrupted connection from load or driver behavior without additional circuit evidence. It also cannot establish a mechanical injector blockage or justify a fuel-system repair purely from the electrical classification.

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 557 · GM PDF, physical page 558.