EVAP Canister Purge Valve

PRINCIPLE OF OPERATION, EVAP CANISTER PURGE VALVE

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EVAP Canister Purge Valve--consists of a solenoid valve mounted on the vacuum hose between the evaporative emission canister and the intake manifold after the throttle.

The valve is supplied with current from the main relay and controlled from pin 27 of the control module. The same lead is connected to pin 21 of the control module. By measuring the voltage on pin 21, the control module determines whether operation is electrically correct. The valve is open when not supplied with current and closed when grounded by the control module.

The valve is supplied with an 8 Hz PWM signal and starts working as soon as Lambda control is activated, engine coolant temperature is above 20°C and intake manifold pressure below 90 kPa.

The control module starts the purging phase by breaking the valve circuit for a brief moment and then gradually increasing the time. The reason for this is that the Lambda control system must have time to compensate for the additional fuel. The valve operates for 4 1/2 minutes, followed by a pause of 1/2 minute, then 6perates for 4 1/2 minutes again, and so on.

During the 1/2 minute the valve is not in operation, spot adaptation will take place if the conditions for this are fulfilled. Adaptation cannot take place when the valve is in operation since the amount of additional fuel is then unknown.

If there is a break in the valve circuit, the CHECK ENGINE lamp malfunction indicator lamp (MIL) in the main instrument display will light up.

If the valve jams in the open position, malfunctioning of the oxygen sensor will result and cause the MIL in the main instrument display to light up.