Evaporative Emission (EVAP) System Components

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The EVAP system consists of the following components:

Capless Fuel Fill

Most vehicles have a capless fuel fill design. There is no fuel fill cap to remove. A flapper valve closes to seal this interface once the fill nozzle is removed.

Evaporative Emission Canister

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

G58 Evaporative Emission Purge Pump

Purge capacity is being reduced by technologies which improve fuel economy. The G58 Evaporative Emission Purge Pump is used to purge stored vapors from the Evaporative Emission Canister and is required to increase the purge volumes to meet LEV 3 Evaporative Emission requirements. The G58 Evaporative Emission Purge Pump has an integral pressure sensor for controlling purge vapors from the canister.

Q12 Evaporative Emission Purge Solenoid Valve

The Q12 Evaporative Emission Purge Solenoid Valve controls the flow of vapors from the Evaporative Emission system to the induction system. The Q12 Evaporative Emission 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. The Q12 Evaporative Emission Purge Solenoid Valve will also be opened during some portions of the Evaporative Emission diagnostic test when the engine is running, allowing vacuum to enter the Evaporative Emission system.

Q13 Evaporative Emission Canister Vent Solenoid Valve

The Q13 Evaporative Emission Canister Vent Solenoid Valve controls fresh airflow into the Evaporative Emission Canister. The Q13 Evaporative Emission Canister Vent Solenoid Valve is normally open. The Q13 Evaporative Emission Canister Vent Solenoid Valve is closed only during Evaporative Emission diagnostic testing performed by the ECM such as the large leak and engine off natural vacuum test.

B150 Fuel Tank Pressure Sensor

The B150 Fuel Tank Pressure Sensor measures the differential pressure between the fuel tank and the atmosphere. Depending on the vehicle, the sensor can be located in the vapor space on top of the fuel tank or in the vapor tube on top of the tank. A high fuel tank pressure sensor voltage reading indicates vacuum. A low fuel tank pressure sensor voltage reading indicates pressure.

Fuel Fill Cap

The fuel fill cap seals the filler neck, it may contain a vacuum relief. A fuel filler cap that is not properly sealed may cause a malfunction in the emission system.

Fill Limit Venting Valve

The fill limit venting valve acts as a shut off valve during refueling. The fill limit venting valve has the following characteristics:

Is located on the inside top of the fuel tank
Is not serviced separately
Controls the fuel tank fill level by closing the primary vent from the fuel tank and forcing the fuel fill nozzle to shut off
Prevents liquid fuel from exiting the fuel tank via the Evaporative Emission Vapor Tube to the canister
Provides fuel-spillage protection in the event of a vehicle rollover by closing the vapor path from the tank to the Evaporative Emission Canister

Vapor Recirculation Tube

A vapor path between the fuel fill pipe and the vapor tube to the carbon canister is necessary for Vehicle On-board Diagnostics to fully diagnose the Evaporative Emission system. It also accommodates service diagnostic procedures by allowing the entire Evaporative Emission system to be diagnosed from either end of the system.

The On-Board Refueling Vapor Recovery System is designed to capture fuel vapors during the vehicle refueling operation. The Vapor Recirculation Tube transports the fuel vapor to the Evaporative Emission Canister for use by the engine.