Diagnostic article Generic OBD-II
P20A2: low purge-valve feedback is evaluated with the driver off
GM P20A2 uses a short-to-ground signature on the reductant purge low-side driver and a different persistence period from the high-circuit fault.
Read before applying this article
Documented application
GM 2015 15OBDG04 Engine Diagnostics, cited purge-valve low-side driver low-voltage monitor. Exact wiring, vehicle fitment and safe isolation procedure are not supplied by the parameter table.
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.
P20A2 is the low-voltage electrical diagnostic for the reductant purge-valve driver in this GM table. It identifies a low feedback voltage while the low-side driver is commanded off, which the source classifies as a short-to-ground signature.
Do not omit the off command
Low voltage can have a different meaning when a low-side driver is intentionally on. The stored off-state command is therefore important evidence, not an incidental detail of the fault description. The monitor also requires ignition on, completed controller initialization and the specified battery-voltage qualification above 10.5 V.
The low-circuit fault must persist for two seconds, with a 0.01-second monitoring rate when its enabling conditions are satisfied. The nearby high-circuit diagnosis has a different commanded state and duration. Their criteria should not be exchanged simply because both concern the same valve.
Locate the electrical cause before judging flow
Preserve command, feedback, supply and related fault information. The controller's short-to-ground classification does not identify the exact wire, connector or internal component responsible. The matching vehicle wiring procedure is needed to isolate that.
This code is also not proof that reductant pressure failed to reduce; that is a separate performance question. The table supplies no valve replacement instruction or terminal-level test setup. Professional verification should establish appropriate feedback in the relevant commanded state and account for the dosing system's pressure and electrical precautions before any physical intervention.
Source and applicability
GM 2015 15OBDG04 Engine Diagnostics, cited purge-valve low-side driver low-voltage monitor. Exact wiring, vehicle fitment and safe isolation procedure are not supplied by the parameter table.
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 Low
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