Diagnostic article Generic OBD-II
P27C1: Valve three stuck-off needs a second path to validate rod feedback
P27C1 checks rods three and four through an integrity routine, then uses another valve to confirm that position feedback can report movement.
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.
P27C1 corresponds to shift solenoid three hydraulically stuck off in this controller. Its integrity routine makes small test movements on rods three and four with selected hydraulic routing. The purpose is to assess actuation capability, not to perform a complete gear engagement.
No movement is only the first finding
The relevant valve-three test cases show movement no greater than 100 micrometres. That makes ineffective hydraulic actuation suspicious, but could also resemble position feedback stuck at a value. The continuation uses valve four to produce movement above 100 micrometres on one of those rods, validating that the feedback can respond.
The alternate path is therefore part of the diagnosis, not an optional extra observation. A single flat position trace cannot establish the complete stuck-off result.
Confirm the routine’s completion
The integrity sequence is invoked by recovery logic or a startup mismatch between retained gear state and sensed engagement. Verification needs evidence that its relevant cases actually executed. A drive without the routine is not equivalent to a completed test suite. The source supports a specific hydraulic classification but does not supply a safe generic method for commanding intrusive rod movements or isolating a replacement solenoid.
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 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