Diagnostic article Generic OBD-II
P27CA: Valve-four stuck-on requires unexpected travel and partner relaxation
P27CA evaluates rods three and four after hydraulic routing changes, rather than diagnosing a stuck valve from one position.
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Documented application
2025 GM 25OBDG07A Part 2 documented monitor only; its application-matrix filename join is unresolved. No model, engine or universal calibration applicability is inferred.
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 cited P27CA strategy concerns shift solenoid four hydraulically stuck on. It watches the rod response when the selector changes hydraulic routing. Persistent valve pressure can produce unintended travel on one rod while another rod relaxes, giving the controller a paired pattern to evaluate.
Commanded force must be absent
Both rod-three and rod-four force targets must be zero. The source then looks for at least 1,000 micrometres of unintended movement and at least 125 micrometres of companion relaxation within 200 ms of the selector-target change. The roles depend on the target routing state.
Relevant position-sensor and valve electrical faults must not be active. Without those conditions, movement might represent an intentional command or unreliable feedback rather than the documented stuck-on event.
Verification preserves the relationship
Record selector target, both rod positions and force requests together. A single position sample or a normal subsequent shift cannot reconstruct the original transition. The generic solenoid-R label is mapped to valve four only in this source’s implementation. The table supports the hydraulic classification but does not describe a universal mechanical repair or authorize manually reproducing the intrusive sequence outside the applicable service procedure.
Document scope and source
2025 GM 25OBDG07A Part 2 documented monitor only; its application-matrix filename join is unresolved. No model, engine or universal calibration applicability is inferred. These figures explain the cited controller logic, not a vehicle-specific repair instruction. Match the vehicle’s service information before applying them.
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
Pressure Control Solenoid R Stuck On
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