Diagnostic article Generic OBD-II
P27BA: A stuck-on shift valve is inferred from two rods moving differently
P27BA uses unintended movement and relaxation around a selector change to diagnose shift solenoid two hydraulically stuck on.
Read before applying this article
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.
P27BA corresponds to shift solenoid two hydraulically stuck on in the cited transmission. The controller watches rods one and two during and shortly after a selector-position change. Pressure that remains applied can move one rod unintentionally while the other relaxes as the hydraulic routing changes.
The movement pattern is the evidence
The table combines at least 1,000 micrometres of unintended movement on one rod with at least 125 micrometres of relaxation on its partner. Which rod plays each role changes with the selector target. The observation window is within 200 ms of the selector command change.
Both rod-force targets must be zero, and relevant position-sensor and valve electrical faults must be absent. Thus ordinary commanded rod travel is not equivalent to this stuck-on pattern.
Verification must preserve both channels
Capture the selector transition and both rod responses together. One moving position trace alone loses the corroborating relaxation evidence. The source’s generic solenoid-N label is mapped to shift solenoid two only for this implementation. It does not identify a universal transmission component location. The summary explains the hydraulic inference but is not a procedure for manually forcing selector changes or replacing a valve without the applicable service tests.
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 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