Diagnostic article Generic OBD-II
P20A0: reductant purge-driver feedback is wrong while commanded off
The GM P20A0 example diagnoses an open-circuit signature on the purge-valve low-side driver, after supply and initialization conditions are met.
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Documented application
GM 2015 15OBDG04 Engine Diagnostics, cited reductant purge low-side driver monitor. No per-code vehicle assignment or terminal-level test 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.
P20A0 is an electrical check of the reductant purge-valve low-side driver in this GM calibration. The relevant observation is low feedback voltage while the driver is commanded off. The table associates that signature with an open-circuit condition; it is not a measurement of whether reductant pressure actually decreased.
Command state is essential evidence
The diagnostic requires ignition on, completed controller initialization and a battery-voltage condition above 10.5 V for the specified qualifying period. The fault must persist for three seconds while the monitor runs at a 0.1-second rate, subject to its general enable and inhibition tables.
A feedback voltage without the driver's commanded state cannot establish this diagnosis. The expected observation when the low-side driver is on differs from the observation used for an open-circuit check while it is off.
Separate an electrical signature from valve movement
A technician should preserve command, feedback and supply information, then use the applicable wiring procedure to identify where continuity has been lost. The code does not prove that the purge valve is mechanically stuck or that the entire dosing module requires replacement.
The source's parameter boundary describes the controller's open-circuit classification. It is not a substitute for the correct connector, isolation state or measurement procedure. Reductant systems can retain pressure and have application-specific electrical arrangements. Verification should use the matching service information and demonstrate correct feedback in the commanded state, rather than relying only on an erased fault record.
Source and applicability
GM 2015 15OBDG04 Engine Diagnostics, cited reductant purge low-side driver monitor. No per-code vehicle assignment or terminal-level test is inferred.
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
Reductant Purge Control Valve A 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