Evaporative Emissions

^ M54B2.5 Low Emission Vehicle (LEV)
^ M54B3.0 Ultra Low Emission Vehicle (ULEV)








Evaporative Emissions: The control of the evaporative fuel vapors (Hydrocarbons) from the fuel tank is important for the overall reduction in vehicle emissions. The evaporative system has been combined with the ventilation of the fuel tank, which allows the tank to breath (equalization). The overall operation provides:
^ An inlet vent, to an otherwise sealed fuel tank, for the entry of air to replace the fuel consumed during engine operation.
^ An outlet vent with a storage canister to trap and hold fuel vapors that are produced by the expansionaporation of the fuel in the tank, when the vehicle is stationary.
The canister is then purged using the engine vacuum to draw the fuel vapors into the combustion chamber. This "cleans" the canister allowing for additional storage. Like any other form of combustible fuel, the introduction of these vapors on a running engine must be controlled.
The ECM controls the Evaporative Emission Valve which regulates purging of evaporative vapors. The evaporative system must be monitored for correct purge operation and Leak Detection.

On-Board Refueling Vapor Recovery (ORVR DM TL Equipped Vehicles): The ORVR system recovers and stores hydrocarbon fuel vapor that was previously released during refueling. Non ORVR vehicles vent fuel vapors from the tank venting line back to the filler neck and in many states reclaimed by a vacuum receiver on the filling stations fuel pump nozzle.
When refueling an ORVR equipped vehicle, the pressure of the fuel entering the tank forces the hydrocarbon vapors through the Filling Vent Valve (2) and the large tank ventilation line (4) into the Carbon Canister (6). The HC is stored in the Carbon Canister and the system can then "breath" through the DM TL (7) and the filter (8).

Note: A small diameter connection to the filler neck is provided by the Mushroom Valve T fitting (5). This is necessary for checking the filler cap/neck during Evaporative Leak Testing.

The ventilation continues until the rising fuel level lifts the float in the Filling Vent Valve (2) and closes the outlet. When the ventilation outlet is closed, a pressure cushion (vapor area) is created in the fuel tank. This creates a backup of fuel into the filler neck and the tank is full.
This leaves a vapor area of approximately 6 liters above the fuel level. This area provides integral liquid/vapor separation. The vapor condensates separate and drain back into the fuel. The remaining vapors exit the fuel tank (when sufficient pressure is present) through the Operating Vent Valve (3) to the Carbon Canister.

Note: The Operating Vent Valve is also equipped with a protection float in the event of an overfill situation.





Carbon Canister: As the hydrocarbon vapors enter the canister, they will be absorbed by the active carbon. The remaining air will be vented to the atmosphere through the end of the canister, DM TL and filter, allowing the fuel tank to breath.
When the engine is running, the canister is purged using intake manifold vacuum to draw air through the canister which extracts the HO vapors into the combustion chamber.
The Carbon Canister with DM TL and air filter are located at the right rear underside of the vehicle, below the luggage compartment floor.





Evaporative Emission Valve: This ECM controlled solenoid valve regulates the purge flow from the Carbon Canister into the intake manifold. The ECM Relay provides operating voltage, and the ECM controls the valve by regulating the ground circuit. The valve is powered open and closed by an internal spring.
If the Evaporative Emission Valve circuit is defective, a fault code will be set and the Malfunction Indicator Light will illuminate when the OBD 11 criteria is achieved.
If the valve is mechanically defective, a driveability complaint could be encountered and a mixture related fault code will be set.





Evaporative Leakage Detection (DM TL): This component ensures accurate fuel system leak detection for leaks as small as 0.5 mm by slightly pressurizing the fuel tank and evaporative components. The DM TL pump contains an integral DC motor which is activated directly by the ECM. The ECM monitors the pump motor operating current as the measurement for detecting leaks.
The pump also contains an ECM controlled change over valve that is energized closed during a Leak Diagnosis test. The change over valve is open during all other periods of operation allowing the fuel system to breath through the inlet filter. The DM TL is located under the luggage compartment floor with the Carbon Canister.








1. In its inactive state, filtered fresh air enters the evaporative system through the sprung open valve of the DM TL.
2. When the DME activates the DM TL for leak testing, it first activates only the pump motor. This pumps air through a restricter orifice (0.5 mm) which causes the electric motor to draw a specific amperage value. This value is equivalent to the size of the restricter.
3. The solenoid valve is then energized which seals the evaporative system and directs the pump output to pressurize the evaporative system.
^ A large leak is detected in the evaporative system if the amperage value is not achieved.
^ A small leak is detected if the same reference amperage is achieved.
^ The system is sealed if the amperage value is higher than the reference amperage.





Since MY 2002, a heating element is integrated in the DM TL pump to eliminate condensation. The heater is provided battery voltage with KL15 and the ECM provides the ground path.