P27C2: Valve three stuck-on is a paired rod-response pattern

The P27C2 monitor identifies shift solenoid three hydraulically stuck on by examining the response to a selector change. In this implementation, persistent pressure can create unintended movement of one rod and relaxation of the other when routing changes. The paired response is stronger evidence than a single unexpected position change.

What the controller compares

For rods three and four, the source requires at least 1,000 micrometres of unintended travel on one side and at least 125 micrometres of relaxation on the partner. The roles switch with the selector target. The observation is made within 200 ms of the target change.

The rod-force targets must be zero, and the relevant sensor and pressure-valve electrical faults must be absent. Those conditions distinguish the fault pattern from intentional shifting or untrustworthy feedback.

Verification needs the transition

Retain the selector command, both rod positions and force targets on the same timeline. A later stationary position cannot reconstruct the paired movement that caused the classification. The code’s generic solenoid-P name does not map universally to a physical valve. Use the actual transmission’s service procedure; this monitor summary is not an instruction to reproduce hydraulic movements manually or replace a component from the title alone.

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.

GM physical PDF page 1021.