Evaporative Emissions System: Description and Operation
Fuel and Emissions System Description - EVAP Control System
Evaporative Emission (EVAP) Control System
Refer to the system diagram to see the functional layout of the system.
EVAP Canister
The EVAP canister temporarily stores fuel vapor from the fuel tank until it can be purged back into the engine and burned (refer to the system diagram to see the functional layout of the system).
EVAP Canister Purge Valve
When the engine coolant temperature is below 140 °F (60 °C), the PCM turns off the EVAP canister purge valve which cuts vacuum to the EVAP canister.
Fuel Tank Pressure (FTP) Sensor
The FTP sensor converts fuel tank absolute pressure into an electrical input to the PCM.
EVAP Canister Vent Shut Valve
The EVAP canister vent shut valve is on the EVAP canister.
The EVAP canister vent shut valve controls the venting of the EVAP canister.
Evaporative Emissions (EVAP) Control System Diagram
The EVAP control system minimizes the fuel vapor escaping to the atmosphere. Vapor from the fuel tank is temporarily stored in the EVAP canister until it can be purged from the canister into the engine and burned. The purge amount and timing is duty controlled by the PCM by operating the EVAP canister purge valve. This system is operated whenever the engine coolant temperature is above 140 °F (60 °C). For this turbo engine model, there are two different purge flow passages, because the intake manifold pressure can be positive (boost pressure) or negative (vacuum pressure).
Purge to the throttle body
When the engine is under a low load condition, the pressure inside the intake manifold is negative (vacuum pressure). The vacuum pressure of the intake manifold opens non-return valve A and closes non-return valve B. Under this condition, the purge air flows from the EVAP canister through the EVAP canister purge valve and non-return valve A, into the throttle body.
Purge to the intake air duct (turbocharger inlet pipe)
When the engine load increases, the pressure after the turbocharger changes to positive pressure due to turbocharger operation. The boost pressure at the throttle body closes non-return valve A, and due to the boost pressure at the charge air cooler, some part of the compressed air flows through the passage from the air bypass valve base to the intake air duct (turbocharger inlet pipe). When the speed of that compressed air increases at the EVAP canister purge nozzle, it draws the purge air from the EVAP canister side. The non-return valve B opens by this vacuum pressure, and the purge air flows from the EVAP canister through the EVAP canister purge valve and non-return valve B, into the intake air duct (turbocharger inlet pipe).
Purge to the both intake air duct (turbocharger inlet pipe) and the throttle body
When the engine is under a mid load condition, the pressure after the turbocharger is positive due to the turbocharger operation, but the pressure at the intake manifold is negative because the throttle valve is nearly closed. Under this condition, both non-return valves A and B open and the purge air flows from the EVAP canister through the EVAP canister purge valve and non-return valves A and B, into the throttle body and the intake air duct (turbocharger inlet pipe).
Fuel Cap Warning Message
The PCM detects a loose or missing fuel fill cap as an evaporative system leak and alerts the driver by showing a warning message in the gauge display.
First drive cycle
The first time a leak is detected a "TIGHTEN FUEL CAP" (multi-information display model) ("CHECK FUEL CAP" (information display model)) message in the gauge display (A). To scroll to another message, press the select/reset button. The "TIGHTEN FUEL CAP"/"CHECK FUEL CAP" message appears each time you restart the engine until the system turns the message off. Turn the engine off then replace or tighten the fuel fill cap until it clicks at least once.
To make the message go off (with the HDS)
Procedure
- Tighten the fuel fill cap until it clicks.
- Clear the Pending DTC with the HDS.
- Verify there is no leak by doing the EVAP FUNCTION TEST in the INSPECTION MENU with the HDS.
To make the message go off (without the HDS)
Procedure
- Tighten the fuel fill cap until it clicks.
- Start the engine, then turn the ignition switch to LOCK (0).
- Repeat step 2 two more times.