Diagnostic article Generic OBD-II
P27CD: Valve-four open-load uses the circuit’s off-state response
P27CD checks whether the synchronizer valve-four load path holds the driver node in its expected state when switched off.
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.
P27CD is the open-load electrical monitor for synchronizer actuation valve four in this transmission. The off-state load should pull the driver’s monitored node toward battery supply. The driver attempts to regulate the node at a lower diagnostic voltage with a very small current; success indicates the expected load path is absent.
A failed shift is not the same test
The source requires more than 5 ms of low-side-output off time and at least 150 ms confirmation. Its question is electrical continuity under a controlled state, not whether hydraulic pressure moved a synchronizer successfully.
Battery voltage must be within the documented operating window and the system outside safe state. P0882 and P0883 disable the monitor. Those prerequisites should be retained when interpreting an apparently successful follow-up.
The useful next distinction
Determine whether the open-load report recurs during the required off interval, using the applicable service method and actual valve-four circuit identity. A normal voltage while energized does not answer that question. The summary does not reveal whether an open coil, disconnected path, harness issue or driver behavior produced the classification. It provides no universal terminal assignment from the generic solenoid-R name.
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 R 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