(h) Evaporative Emission (EVAP) Purge System Vacuum Switch

(h) Evaporative Emission (EVAP) Purge System Vacuum Switch
The EVAP system uses a switch located in the purge line between the canister and the purge valve to detect when purge is occurring. 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 the 12 volt signal to the control module. A Tech 2 display will indicate that purge is occurring.

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. (Refer to EVAP Vacuum Switch in On-Vehicle Service Procedures.)





The EVAP system uses a fuel tank pressure sensor, located on top of the fuel tank sender unit, in order to detect when the EVAP system is purging. The fuel tank pressure sensor detects the flow from the engine through the EVAP canister purge solenoid valve. When the EVAP system is not purging, the fuel tank pressure sensor will detect no change in fuel tank vacuum. When the EVAP system is purging, the fuel tank pressure sensor will detect a vacuum in the fuel tank. A change in fuel tank pressure will be displayed on the scan tool.

If any of the following EVAP malfunctions are present:
- Leak
- Plug
- Malfunctioning Fuel Tank Pressure Sensor

One of the following DTCs will set:
- P0440
- P0442
- P0446
- P0452
- P0453
- P1441

If any of these DTCs are set, go to the DTC table for diagnosis.