Diagnostic article Generic OBD-II
P2821: how a park-lock valve is diagnosed hydraulically stuck on
P2821 identifies a park-lock engagement valve that does not produce the expected hydraulic-off response in this GM monitor.
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Documented application
Documented 2025 GM gm-2025-07a-2 monitor only; vehicle, engine and controller applicability must be established separately. The download-index/application-matrix filename join is unresolved; no model or engine 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.
P2821 has a generic solenoid-J stuck-on label, but the cited 25OBDG07A Part 2 table describes the park-lock engagement valve. Its diagnostic uses commanded hydraulic states and park-lock position, rather than assuming that an electrical circuit code proves a stuck valve.
A controlled release sequence
During the documented disengagement routine, the controller first opens the parking lock using both hydraulic valves. It then energizes the hold solenoid so the lock remains mechanically held away from engagement if piston pressure is removed. The engagement valve is commanded hydraulic-off while the latching valve remains hydraulic-on.
The expected position changes from open to hold. If the sensor continues reporting open after the engagement-valve off test, the controller diagnoses a hydraulic stuck-on response. The listed confirmation timer exceeds 200 milliseconds. Conditions include vehicle speed no greater than 3 km/h, oil temperature no higher than 120°C and battery voltage at least 10 volts. Relevant park-system electrical faults must be absent.
Read position and command together
An “open” park-lock position is normally desirable when driving, but becomes the failure observation during this specific pressure-draining step. Looking at position without the active routine can therefore reverse the interpretation. The hold solenoid also explains why an off command does not require the parking lock to become fully locked in this test.
The source describes additional engagement strategies on following pages; their criteria should not be merged into this release sequence. Professional diagnosis should reproduce the correct routine safely and confirm the expected position transition before declaring the hydraulic behavior restored.
Source and applicability
Documented 2025 GM gm-2025-07a-2 monitor only; vehicle, engine and controller applicability must be established separately. The download-index/application-matrix filename join is unresolved; no model or engine is inferred. GM monitor table, PDF page 999.
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 J 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