What does it mean?
OBD II fault code P0441 is defined as “Evaporative Emission Control System Incorrect Purge Flow”, and is set when the PCM (Powertrain Control Module) detects that a part of the EVAP (Evaporative Emission Control) system is not working correctly. Typical EVAP systems consist of the fuel tank, fuel filler cap, pressure and flow sensors, a charcoal canister, purge valve with a control solenoid, fuel and vacuum lines, fuel vapor hoses, and electrical wiring / connectors.
Various sensors in the EVAP system converts changes in the pressure or flow rate in the system into signal voltages, which the PCM compares with pre-defined values. When the PCM receives a signal voltage that does not conform to the expected value for any given operational condition, a code will be stored, and a warning light might illuminate.
Note that while most on most applications a warning will be triggered on the first failure, a few applications require several fault cycles before a warning light is triggered. The function of the EVAP system is to capture fuel vapors before they can escape into the atmosphere.
Fuel vapors are collected and either passed through a charcoal canister in which the activated charcoal stores the vapors, before being passed to the inlet tract through a network of hoses to be burned as part of the air/fuel mixture when operational conditions allow this to happen.
The rate of flow of the collected vapors is controlled by a purge valve that opens or closes gradually in response to signals sent to it from the PCM, which in its turn, receives pressure-based signals from pressure sensors in the EVAP system. Note that the rate at which fuel vapors are delivered to the engine for combustion is not constant.
For instance, when the engine is under a heavy load that requires additional fuel, the PCM will command the EVAP system to deliver large amounts of fuel vapor. Conversely, when the engine is running at a steady load, the available fuel vapors will be released slowly, and gradually, with the oxygen sensors serving to alert the PCM when the air/fuel mixture reaches an overly-rich condition, at which point the PCM will reduce the vapor flow rate.
The image below shows a simplified schematic of a typical modern EVAP system.