The logic module uses this solenoid on 1986 and earlier models to shut off the purge canister when the engine is cold. The purge canister collects fuel vapors from the fuel tank and carburetor float chamber (if applicable) so that they are drawn into the intake manifold. Once the engine temperature is above 145^F, the solenoid is de-energized and vapors are drawn from the canister into the intake. A check valve prevents positive pressure from reaching the canister. For 1987 and later models (except those without an EGR and the L-body), this solenoid also took on the role of operating the EGR valve. When the engine temperature is is below 80^F, is above 80^F for less than 7 seconds, at idle, or during boost, the solenoid is activated. This closes the EGR valve and stops gases from being drawn from the purge canister.
When the logic module is turning on or off the solenoid, it momentarily checks the output of the solenoid driver to see if it is responding the way it should. If it does not see about 0V when on (open circuit) or 12V when off (short circuit), a fault code 31 is stored.
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Copyright © 1996-2003 Russ W. Knize.