Here are some potential culprits:
* Gas Cap Still Faulty: While less likely after replacement, it's possible you received a defective replacement gas cap. Try a different brand or ensure it's properly seated and sealing.
* Evaporative Emission (EVAP) System Purge Valve: This valve controls the flow of fuel vapors from the charcoal canister back into the engine to be burned. A faulty valve can prevent proper purging, triggering the P0440 code.
* Charcoal Canister: The canister stores fuel vapors until they can be purged. If the canister is damaged, clogged, or filled with debris, it won't function correctly.
* EVAP System Hoses and Lines: Cracks, leaks, or loose connections in the hoses and lines that make up the EVAP system can cause a leak and trigger the code. These are often difficult to spot visually and may require a pressure test.
* Vapor Pressure Sensor: This sensor monitors the pressure within the EVAP system. A malfunctioning sensor can lead to inaccurate readings and trigger the code.
* Fuel Tank Pressure Sensor: Similar to the vapor pressure sensor, this one monitors pressure within the fuel tank itself.
What to do next:
1. Double-check the gas cap: Ensure it's from a reputable source, correctly seated, and sealing properly.
2. Have a professional diagnostic test performed: A mechanic can use a scan tool to gather more specific data beyond just the P0440 code. This can help pinpoint the faulty component within the EVAP system more precisely. A pressure test of the EVAP system is often crucial.
3. Visual inspection: While difficult, a mechanic might be able to visually inspect the hoses and lines for cracks or leaks.
Ignoring the issue could lead to further problems and potentially impact your vehicle's emissions testing. Professional diagnosis is recommended to avoid unnecessary part replacements.
