P21D1: Understanding the cylinder 3 injector B open-circuit category

P21D1 describes cylinder 3 injector B circuit/open in the generic catalog. The GM monitor row identifies injector channel 3 and checks its electrical load while the power stage is inactive. This is a circuit-recognition test, not a measurement of fuel injected into the cylinder.

The voltage window has a specific diagnostic role

The documented open-load observation is an output voltage from 3 V inclusive to below 5 V. Three events are listed for maturation. Engine speed must be at least 80 rpm, and the battery supply must meet the row's 10.9–25.5 V limits and referenced inhibition rules.

Those details separate this test from the neighboring high-circuit check, which looks at current with the stage active. Swapping one test state for another would change what the observations mean.

What to establish before selecting a repair

Confirm the actual injector B arrangement and channel mapping using the engine's applicable documentation. Even where the generic and document numbers match, that does not establish a connector location or whether a particular engine has the same injector configuration.

The useful diagnostic record contains the open-load status, stage state and whether the monitor was allowed to run. A drivability symptom alone cannot show that this electrical criterion was met. The source does not isolate an interrupted wire, an injector winding or the internal driver. Locate the electrical cause through the correct circuit procedure before treating the code as evidence that a mechanically faulty injector must be replaced.

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 556.