P0459: Purge-solenoid high feedback during an active low-side command

P0459 identifies a high fault in the EVAP purge-control circuit. For the cited GM system, the controller checks the canister purge solenoid's low-side driver for a short to power when the output is on. It evaluates whether the electrical feedback matches the commanded state.

This is not a purge-flow measurement

A driver-high result does not independently establish how much vapor reaches the intake or whether the valve seals mechanically. The circuit response must be evaluated first. The page defines a controller short-to-power specification corresponding to less than 0.5 Ω between output and controller power, without supplying a universal field-test procedure.

Powertrain-relay voltage must exceed 11 volts. The controller uses twenty failures out of twenty-five samples at 250-millisecond intervals and lists Type B, two-trip behavior. Command timing is therefore relevant when interpreting a stored event or comparing a captured voltage trace.

Confirm the on-state response

Retain command, supply and feedback information together. A high value observed with the output off cannot simply be judged by this on-state criterion. Use the actual vehicle's circuit procedure to distinguish the affected connection, harness, actuator or driver path.

After correction, confirm the completed circuit-high monitor passes while its prerequisites are met. An EVAP leak-test pass alone does not reproduce this electrical test. The document does not justify replacing the purge valve solely because P0459 appears.

Source and applicability

This explanation is limited to the 2025 GM 25OBDG03A monitor on page 298. Its thresholds are calibration examples, not universal specifications. Confirm the vehicle, engine and controller procedure before applying them.