P21E2: A low-circuit injector code whose document channel differs from its cylinder label

P21E2 is generically cylinder 4 injector B circuit low. The corresponding GM row is labeled injector 2, and the cited pages do not establish the physical mapping between those naming systems. This limitation matters before any circuit or component is selected.

What the controller’s table actually reports

The low-circuit row is described as a short-to-ground electrical fault. It evaluates an output-voltage quantity above 5 V with the power stage inactive. That is an internal diagnostic definition, not a universal terminal voltage or a reason to reverse the code's electrical category.

Three events are required in the row, with engine speed at least 80 rpm and a defined battery-voltage window. The monitor also depends on referenced inhibition conditions.

Preserve the category while resolving the channel

The source's injector-2 group has different criteria for open load and high-circuit failure. An open-load result cannot be substituted for this low-circuit classification merely because both are evaluated around an inactive stage.

Retain the exact code, controller identity and diagnostic state, then establish the correct physical path from the vehicle documentation. The source does not identify a particular wire, injector element or ECU output as defective. It also provides no fuel-flow measurement. A repair based on the generic cylinder number alone could address the wrong channel despite correctly recognizing that the failure is electrical.

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.