P2418: EVAP switching-valve control circuit has an open signature

P2418 diagnoses the switching valve's electrical control path in the reviewed GM conventional vented EVAP system with fuel tank zone module. The fault is an open-circuit signature, not a conclusion that the valve is mechanically stuck open.

Electrical open versus valve position

The controller evaluates its low-side driver voltage while the output is powered off. Voltage outside the accepted range indicates an open electrical path. The documented design specification is impedance above 200 kilohms between the output and controller ground.

An electrical open and an open valve are different findings. This row does not measure valve travel or determine the vapor path's physical state, so the code name should not be converted into a mechanical diagnosis.

Conditions for meaningful evidence

No EVAP-device communication fault may be active. The diagnostic uses 50 failed samples out of 63, at 250 milliseconds per sample. Preserve communication status and the output's off command when comparing the recorded event with later observations.

The source does not provide a complete voltage-enable specification in this row; borrowing a voltage threshold from another EVAP code would go beyond the evidence. Likewise, the impedance figure is a controller specification rather than an instruction to test a live circuit.

Verification should follow the applicable switching-valve circuit procedure and demonstrate an acceptable off-state response with monitor completion. The documented response is Type B, two trips. This information does not identify a particular connector, authorize valve replacement or prove a fuel-vapor leak.

Source and applicability

The documented control architecture and calibration require confirmation for the vehicle being diagnosed. GM diagnostic table, PDF page 649.