Catera V6-3.0L VIN R (1997)
Purge Flow Sensor: Description and Operation
Description
The EVAP system uses a switch located in the purge line between the canister and the purge valve in order to detect when a purge occurs. This switch
senses the flow from the engine through the purge valve. When no purge is present, the switch is closed, applying a 12 volt signal to the control module
as a NO PURGE signal. When canister purging occurs, the switch opens, interrupting off the 12 volt signal to the control module. A scan tool display
will indicate that purge is occurring.
System Faults
Clogging of the canister fresh air vent could allow the purge hose between the switch and canister to trap vacuum with the purge valve closed. This
would result in a diagnostic indication of a purge valve stuck open or a vacuum switch failure. Similarly, leaks or blockages in the purge hoses may result
in misdiagnosis of the purge valve or vacuum switch.
When servicing a purge valve diagnostic trouble code, check the canister fresh air vent, vacuum switch and the integrity of all purge hoses prior to
servicing the valve.