The EVAP system (The evaporative emission control system) is responsible for controlling the vapors from the fuel tank so that they enter the engine and are burned instead of being expelled into the atmosphere. It consists of a solenoid that goes into the purge valve and this provides changes in battery voltage.
The ECM (Engine Control Module) inspects the valve by activating the ground circuit, and thus, the purge valve opens at specific times, allowing these gases to enter the engine. Similarly, the ECM controls the ground circuit, which allows troubleshooting.
When the purge solenoid has not been activated, the ECM (Engine Control module) should perceive a high voltage in the ground circuit, when the solenoid is activated or working properly, the ECM should see the ground voltage at a low level, this is very close to 0.
If the Engine Control Module (ECM) does not observe the expected voltages or concludes that there is a short in the circuit, the diagnostic code P0443 is set.