Canister Purge Solenoid: Description and Operation

Evaporation Controls:

PURPOSE
The Evaporative Emission (EVAP) Control System stores vapor generated by the vehicle and regulates its consumption during normal driving conditions. The main purpose of the EVAP system is to prevent fuel vapor from dispelling into the atmosphere.

OPERATION
The EVAP solenoid is controlled by the Powertrain Control Module (PCM). The engine mounted solenoid is normally closed and when certain operating conditions are met the solenoid opens allowing engine vacuum to purge the canister.

LOCATION
The solenoid is located on the top LH side of engine, on valve cover.

CIRCUIT OPERATION
The EVAP solenoid receives 12 volts from the fuse panel. The PCM energizes the EVAP solenoid by grounding CKT 428. When the solenoid is energized it allows the cannister to purge.


PURGE MODE
When a purge mode is commanded, stored fuel vapor is drawn into the inner dip tube through a calibrated orifice at the base of the tube. Any liquid trapped in the liquid well is also drawn into the inner dip tube through a smaller calibrated orifice. Fresh air is drawn into the canister at the top mounted vent.

COMPUTER CONTROL
The PCM operates a solenoid valve which purges the charcoal canister with ported vacuum at the throttle body. Under cold engine, "OPEN LOOP", or idle conditions, the solenoid is de-energized by the PCM, which closes the purge solenoid and blocks vacuum to the canister.

The canister will be enabled (PCM energizes the solenoid) when:
^ Coolant is above 80°C.
^ Closed loop has been achieved for at least 150 seconds.
^ The throttle switch is open.
^ Vehicle speed greater than 20 mph.
^ Engine speed above 100 RPM.
^ Engine metal over temp/low coolant condition is not present.


If the solenoid is closed, (not receiving power or has a stuck plunger), the canister will not purge to the intake manifold. This will prevent the canister from purging fuel vapors and could result in a complaint of fuel odors coming from the engine compartment.