Diagnostic article Generic OBD-II
P21D3: Keeping injector-channel identity separate from a cylinder 5 open-load label
Learn the documented P21D3 inactive-stage check and why the channel mapping must be resolved before testing.
Read before applying this article
Documented application
2025 GM 25OBDG07A Part 2 monitor tables only; model, engine and transmission applicability are not established by the unresolved application-matrix filename join.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
The generic P21D3 definition names cylinder 5 injector B circuit/open. In the cited GM table, P21D3 appears in the group labeled injector 7. Different internal numbering can account for such distinctions, but these pages do not provide the mapping needed to identify a physical injector confidently.
A bounded electrical observation
The row's open-load criterion uses output voltage at least 3 V and less than 5 V while the power stage is inactive. The listed maturation count is three events. Engine speed and supply conditions must also be met; an idle electrical snapshot outside that eligibility is not a completed diagnostic.
The voltage is part of the controller's test definition. It should not be converted into a universal connector-pin specification or used as an instruction to power an injector.
What remains useful despite the mapping limitation
The source clearly distinguishes open load from its channel's low-circuit and high-circuit diagnoses. That allows the observed failure category to be preserved accurately while the physical circuit identity is verified elsewhere.
Retain controller and calibration identification together with the complete code and driver state. Those details are needed to choose the correct wiring information. The monitor does not evaluate fuel pressure, delivery quantity or spray quality, and it cannot isolate a wire, winding or driver as the failed part. Resolving the channel mapping is a necessary step before circuit testing or any component replacement decision.
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 558.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Cylinder 5 Injector B Circuit/Open
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT