Diagnostic article Generic OBD-II
P27B9: Shift solenoid two stuck-off is checked with controlled rod movements
P27B9 uses a synchronizer integrity routine and an alternate actuation path to distinguish absent movement from bad position feedback.
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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 generic solenoid-N performance code P27B9 corresponds to shift solenoid two hydraulically stuck off in this transmission table. The controller’s integrity routine commands small rod movements; it is not intended to engage or disengage complete gears during the test.
Why two rods and another valve matter
The tested pressure valve is exercised with opposite selector states for rods one and two. Movement at or below 100 micrometres across the relevant test cases supports a failure to actuate. The continuation then requires movement above 100 micrometres through an alternative valve path to validate position-sensor operation.
That comparison is essential. No movement from one test alone cannot distinguish an ineffective valve from feedback that fails to report motion.
The routine must actually run
The integrity sequence is triggered by recovery logic or a startup disagreement between retained gear state and sensor evidence. A normal drive that never executes the sequence is not a repeat of its diagnostic tests.
Preserve which cases completed and which alternate movement verified the sensor. The result supports a hydraulic stuck-off classification for this calibration, but the summary is not an instruction to command intrusive transmission movements manually or replace a solenoid without 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 N Performance/Stuck Off
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