P21D6: Understanding the electrical evidence behind a cylinder 8 injector B open code

The generic code list describes P21D6 as cylinder 8 injector B circuit/open. In GM's cited monitor table, the row belongs to injector channel 4. That difference remains an applicability question; it does not establish that either numbering convention is erroneous.

The open-load test is clearly defined

With the power stage inactive, the controller checks for an output voltage at least 3 V but below 5 V. The table specifies three events, engine speed at least 80 rpm and battery voltage inside its stated operating window. Additional inhibiting faults are handled by referenced tables.

The stage state is essential. A current measurement while an injector is being energized belongs to a different electrical assessment and cannot be substituted for this voltage-window test.

Preserve useful evidence while resolving identity

An open-load report is distinct from the low-circuit and high-circuit categories associated with the same document channel. Keep that classification, along with controller identification and the original operating conditions, so the correct physical circuit can be selected from vehicle-specific information.

The source does not map the channel to a connector or prove that an injector winding is the failed part. An interrupted external connection or driver-related behavior cannot be ruled out by the code alone. Nor does the monitor assess fuel spray, quantity or pressure. Resolve the channel mapping before circuit work and evaluate recovery only after the applicable monitor has actually completed.

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 · GM PDF, physical page 557.