Diagnostic article Generic OBD-II
P27C5: An open valve-three circuit is evaluated before hydraulic conclusions
P27C5 checks synchronizer valve three’s off-state load path rather than inferring an electrical opening from a failed shift.
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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.
In this transmission, P27C5 is the electrical open-load diagnostic for synchronizer actuation valve three. The driver checks its monitored node with the low-side output off. A connected load should pull that node toward supply; the diagnostic’s ability to regulate it low with only a small current supports the open-load classification.
The off interval is essential
The table requires more than 5 ms since the output was switched off and at least 150 ms of fault confirmation. The controller must not be in safe state. Battery-related DTCs P0882 and P0883 disable this check, while cranking and stop-key states are outside its normal enable window.
That logic means a valve failing to move a rod is insufficient evidence for P27C5. The hydraulic result and the off-state electrical path are separate measurements.
Useful follow-up evidence
Record the driver’s open-load indication with its command state and supply voltage. A successful energized actuation may be relevant but does not automatically repeat the diagnostic off interval. Identify the actual valve-three circuit through calibration-specific wiring information. The generic solenoid-P label alone cannot locate a terminal or tell whether a coil, connector, harness or output stage caused the reported opening.
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 P Control 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