P21E8: An injector low-circuit diagnosis with cylinder and channel numbering to resolve

The generic definition of P21E8 is cylinder 7 injector B circuit low. The GM monitor row is part of the injector-5 channel group. An internal channel number need not equal a physical cylinder number, and these pages do not provide the mapping that would settle the relationship.

What is supported about the electrical failure

The source classifies the row as a short-to-ground fault. Its output-voltage criterion is above 5 V with the power stage inactive, and it lists three events for maturation. Engine speed and battery supply must meet the stated eligibility requirements.

This combination is an internal driver diagnostic, not a voltage to impose on the injector or expect at an unspecified connector. The document's adjacent open-load and high-circuit rows use different criteria and states.

Choose the physical circuit using vehicle information

The useful diagnostic record includes the exact code, the controller's identity, its calibration and the reported driver category. Those details are needed to select the correct circuit before interpreting a continuity or short test.

The monitor does not identify an injector-flow problem or demonstrate that the injector body is defective. It also cannot locate the electrical cause among harness, load and driver without additional evidence. Preserve the mapping limitation until resolved; testing a convenient cylinder by its generic number is not a reliable substitute. Verification must show that the applicable electrical monitor completed under valid conditions.

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.