When the car is not running, the system catches fuel vapors from the fuel tank, throttle body, and intake manifold that drift up. It holds those fumes in the charcoal canister, then directs them back into the engine to burn during normal operation. The EVAP system includes a charcoal-filled canister, connecting hoses, fuel tank, fuel vapor control valve, fuel tank pressure sensor, fuel cap, fuel vapor opening, ported and intake vacuum. On all models, a box-shaped charcoal canister sits on the frame near the fuel tank, except that the Expedition and Navigator use a round-shaped canister. When the engine switches off, the vapor management valve lets fuel vapors escape from three sources - the fuel tank, throttle body, and intake manifold - and send them to a canister until the engine starts again. When the engine runs, the same valve sends the vapor from the canister through the PCM (powertrain control module) and mixes it with the engine fuel before burning it up. The fuel tank pressure sensor sends the fuel tank interior pressure readings to the fuel monitoring system. This system uses the readings to control EVAP system fuel processes. The system shows EVAP issues by creating special code alerts, such as P0452, P0453, and P1451, pointing at trouble spots. A broken vapor management valve, a defective canister, or cracked hose lines can cause your car to run poorly, be difficult to start, and drive badly. You may find fuel loss or odors from leakage through damaged fuel lines or the throttle body, cracks in the vapor canister, or when the air filter isn't tightly installed. Before starting the engine, check each canister hose for bends, leaks, and breaks. Also look for cracks or damage on the canister itself. You can check for too much pressure in the fuel tank by taking off the gas cap and listening for air escaping, while a special OBD-II tool will give the most correct reading. When pressurized fuel vapor shows up, we must look at two parts: examine the hose and inlet port for blockage and find out if the valve has air access. You test the charcoal canister's tightness by applying pressure and making sure it has air-flow when you release the pressure. Examine all the hoses around the vapor management valve for damage and correct placement. Test the valve's battery power. Label all vacuum hoses connected to the canister before pulling them out, then loosen the mounting clamp bolt to release the canister, and fix it back in place by following these steps in reverse when installing new parts.