EVAP System Components

The EVAP system consists of the following components:

EVAP Purge Solenoid Valve

The EVAP purge solenoid valve controls the flow of vapors from the EVAP system to the intake manifold. The purge solenoid valve opens when commanded ON by the ECM. This normally closed valve is pulse width modulated (PWM) by the ECM to precisely control the flow of fuel vapor to the engine. This valve will also be opened during some portions of the EVAP testing when the engine is running, allowing engine vacuum to enter the EVAP system.

EVAP Canister

The canister is filled with carbon pellets used to adsorb and store fuel vapors. Fuel vapor is stored in the canister until the ECM determines that the vapor can be consumed in the normal combustion process.

Fuel Tank Pressure Sensor

The FTP sensor measures the difference between the pressure or vacuum in the fuel tank and outside air pressure. The ECM provides 5 V reference, ground and signal circuit to the FTP sensor. Depending on the vehicle, the sensor can be located in the vapor space on top of the fuel tank, in the vapor tube between the canister and the tank, or on the EVAP canister. The FTP sensor provides a signal voltage back to the ECM that can vary between 0.15-4.85 V. A high FTP sensor voltage indicates a fuel tank pressure. A low FTP sensor voltage indicates a fuel tank vacuum.

EVAP Vent Solenoid Valve

The EVAP vent solenoid valve controls fresh airflow into the EVAP canister. The EVAP vent solenoid valve is normally closed. This keeps vent fuel vapor sealed in the fuel tank and canister. The EVAP vent solenoid valve is similar to a conventional vent valve, but a conventional vent valve is normally open. This vent solenoid valve is only open for canister purge, refueling, fuel tank pressure sensor correlation or leak check with the EVAP leak detection pump.

Relief Valve

This is a mechanical pressure relieve valve that is part of the vent solenoid valve assembly. It protects the fuel tank by relieving excessive pressure or excessive vacuum that could build up in the sealed fuel tank from environmental changes.

EVAP Leak Detection Pump Assembly

The leak detection pump assembly consists of three main components. These components are integral parts of the EVAP leak detection pump assembly and are not serviceable.

EVAP leak detection pump with reference orifice
EVAP leak detection pump switching valve
EVAP leak detection pump pressure sensor

This leak detection pump assembly is used for FTP sensor correlation and leak checking the EVAP system for small and large system leaks.

EVAP leak detection pump pressure sensor's primary purpose is to perform leak detection diagnostics. The sensor itself is diagnosed by a correlation to barometric pressure based off the MAP sensor.
EVAP leak detection pump 0.51 mm (0.020 in) reference orifice, working in conjunction with the EVAP leak detection pump and pressure sensor. This orifice is used to establish a vacuum reference baseline for diagnosing EVAP leaks
EVAP leak detection pump switching valve switches from a vent position to a pump position depending on the EVAP diagnostics taking place.

Fresh Air Filter

An in-line 5 micron air filter exists between the EVAP leak detection pump fresh air intake and behind the fuel tank fill door pocket to keep the pump hardware from becoming contaminated.

Vapor Recirculation Tube

A vapor path between the fuel fill pipe and the fuel tank is necessary to fully diagnose the EVAP system. It also accommodates service diagnostic procedures by allowing the entire EVAP system to be diagnosed from the either end of the system.

2.54 mm (0.100 in) Orifice in Fuel Fill Vapor Recirculation Pipe

The orifice aids refueling, onboard refueling vapor recovery (ORVR), to avoid canister overload while still allowing closed system leak detection and compliance with ORVR emissions standards.

Fuel Fill Door Lock Solenoid

Prevents fuel fill door opening prior to pressing the Refuel Request Switch.

Fuel Fill Door Position Switch

Provides input to the Hybrid Powertrain Control Module 2 to determine if the door position is open or closed.

Fuel Fill Cap

The fuel fill cap is equipped with a seal and has no relief valve.

Fuel Fill Pipe Check Valve

The check valve on the fuel fill pipe prevents spit-back during refueling.

Refuel Request Switch

NOTE: There is a 30 minute time frame for refueling to occur. If testing the EVAP system the vent solenoid valve will go back to it's normal closed state after 30 min.

NOTE: If more time is needed a second 1 second press of the switch will be required. Or use the scan tool to command the vent solenoid open, if necessary, for additional testing.

Located in the driver's door panel, this switch when pressed for 1 second, puts the EVAP diagnostics into an abort state, opens the vent solenoid valve for refueling and releases the fuel fill door. A message will be displayed on the driver information center. There is a 30 second timer on the door release mechanism allowing sufficient time to press on the fuel door to open it. If 30 seconds lapses before the fuel door is opened a second press of the refuel request switch will be required.