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Evaporative emission system

Evaporative emission system



Evaporative emission canister

The evaporative emission canister is filled with active carbon, which "stores" the fuel vapour coming from the tank until it is exposed of through the purge valve into the intake manifold and used during combustion.

Consequently, the evaporative emission canister is connected to the fuel tank and the intake manifold with hoses but is also in contact with the surrounding air. Air is drawn into the evaporative emission canister through this air connection and sent to the intake manifold, taking with it the fuel vapour in the canister.

EVAP canister purge valve

The purge valve is a solenoid valve located in the vacuum hose between the evaporative emission canister and the intake manifold after the throttle.

The valve is powered from the main relay and is controlled from control module pin 27. On cars without tank integrity diagnostics, the lead is coupled together with control module pin 21. By measuring the voltage on pin 21, the control module can determine whether the function is working electrically.

The valve is supplied with an 8 Hz PWM and starts to work as soon as closed loop is activated, the coolant temperature is above 60°C (140°F) and the intake manifold pressure is below 90 kPa.

The control module initiates the purge with very short ground impulses, the length of which is gradually increased. This is because closed loop must have time to compensate for the addition of fuel. The valve works for 4 1/2 minutes, pauses for 1/2 minute and then works for another 4 1/2 minutes and so on.

Diagnosis

EVAP canister purge valve


• There is no diagnosis for the electrical circuit to the EVAP canister purge valve.