How the code p0441 is diagnosed:
Without a scan-tool: The first part is to check visually for obvious problems: if the gas cap closed properly, there is no cracks or other damage on the charcoal canister and all vacuum hoses related to the EVAP system are properly connected. If no obvious problem is found, the purge valve needs to be tested next. The purge valve should be normally closed. It opens when voltage is applied to its terminals. The purge valve is typically tested with a hand-held vacuum pump. It should hold the vacuum when closed (no voltage) and open fully when voltage is applied; see the procedure below. Sometimes the purge valve may be sticking intermittently but work properly when tested. If there is any suspicion, the purge valve must be replaced; usually it's not very expensive.
If there are other codes, such as P0446 or P0442, they need to be checked out first, as the P0441 can be triggered by the same fault.
With a scan tool: The manufacturer-specific scan tools usually have capability to run the test of the whole EVAP system. With a generic scan tool, the purge valve must be activated and the EVAP system pressure monitored.
