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P0441 is for the performance of the evaporative emissions system purge solenoid. The evap system is what stores fuel vapors from the tank and burns them in the engine, the pure solenoid is what is turned on to draw the vapors in the engine. This code could be caused by a bad purge solenoid, lack of vacuum to it, a leak between the purge solenoid and the rear of the car, damaged or leaking components in the vapor canister and fuel tank area, or a bad natural vacuum leak detector (NVLD). This is the unit that checks the system for leaks. If you've already replaced the purge solenoid then we should be able to rule that out.
If you've checked over the system closely for leaks we should be able to rule a leak out.
Lack of vacuum to the purge solenoid will cause this code to set. There is a vacuum hose that goes from the intake to the purge solenoid. Make sure this hose is in good condition and there is vacuum at the purge solenoid with the engine running.
Also make sure the hose is in good shape from the purge solenoid down to the canister.
The most likely cause for this would be a bad natural vacuum leak detector (NVLD). This is the unit that checks the evap system for leaks. What normally happens is the switch in the NVLD doesn't close when the purge solenoid is commanded on to draw vacuum on the system, and it sets a P0440 or P0441. The NVLD is mounted to the top of the vapor canister on the right side of the fuel tank.