P0499: EVAP vent circuit high reflects a short-to-battery status

P0499 identifies a high condition in the EVAP vent-valve control circuit. The cited GM implementation evaluates a short-to-battery fault reported by the vent power stage through CAN. It therefore carries a specific electrical diagnosis rather than a direct measurement of vapor leakage.

The controller interprets a reported driver fault

The row requires ignition on and the relevant basic enable and inhibit conditions. It specifies a two-second assessment and two-trip reporting. These details describe when the received power-stage status qualifies for this code.

A communication message carrying a fault is different from a missing communication message. The presence of P0499 alone does not establish a CAN wiring problem. Likewise, the high-circuit label does not prove that the vent is mechanically closed or that tank pressure is excessive.

Follow the supply-side electrical evidence

Preserve the exact short-to-battery status and any module-specific supporting information. A fuel-cap inspection or a generic smoke-test result cannot independently confirm that this electrical condition has been corrected.

The source provides no connector assignment, terminal voltage procedure or component replacement instruction. The matching vehicle circuit information is needed to locate the supply-side fault and distinguish load, harness and power-stage possibilities. Use the code to select that diagnostic branch, then verify the monitor under eligible conditions instead of relying only on a cleared warning light.

Source and applicability

This explanation covers the cited GM monitor, not every vehicle carrying this code. The application-matrix filename does not resolve cleanly to this file, so no model or engine fitment is assigned. GM diagnostic table, PDF page 694.