P2420: EVAP switching-valve driver detects a short to power

P2420 is the switching-valve control circuit-high diagnosis for the reviewed GM vented EVAP system with a fuel tank zone module. The monitor evaluates the electrical low-side driver, rather than directly sensing whether the valve is mechanically open or closed.

Fault detection while commanded on

The controller checks voltage during the driver's on state. A value outside its accepted range indicates a short-to-power condition. The source lists less than 0.5 ohm between output and controller power as the controller design specification for that fault signature.

The command state matters because a voltage observation has meaning only in relation to what the driver is trying to do. The impedance figure is not a general instruction to measure a live circuit or an expected valve-coil resistance.

An active fault triggers an extra test

When P2420 is active, the source says the switching valve is commanded on for 15 seconds as an intrusive test. A recorded valve command may therefore belong to fault evaluation rather than the normal vapor-system sequence.

The standard decision uses 50 failed samples out of 63, sampled every 250 milliseconds, and requires the EVAP-device communication fault to be absent. Missing communication changes whether a valid electrical result is available.

Verification should confirm proper on-state driver response and no renewed failure after an applicable completed test. Type B, two-trip behavior is documented. The code does not identify a vapor leak, prove mechanical sticking or establish that the switching valve must be replaced.

Source and applicability

The documented control architecture and calibration require confirmation for the vehicle being diagnosed. GM diagnostic table, PDF page 651.