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Split Purge/Seal EVAP System

Split/Purge Seal Components

  • A Purge solenoid is used to purge fuel vapors and pull system into vacuum for leak detection
  • A Vent solenoid is used to seal the system during EVAP monitor leak testing
  • A Fuel Tank Pressure (FTP) sensor is used to monitor fuel tank pressure/vacuum for leak testing and component monitoring
  • A EVAP Charcoal canister is used to absorb and store fuel vapors
  • A Bypass solenoid is used to isolate the fuel tank and split the system for testing
  • A 2-way valve or Vacuum Cut valve is used to isolate the tank and control airflow under normal system operation.

Split Purge/Seal System Leak Test

  • Operates similar to purge/seal system, but also uses a bypass solenoid and 2-way valve or vacuum cut valve to split the system in half
  • Some manufactures use tank Isolation for EVAP monitor logic, these systems will leak test sections of the system independently
  • During EVAP leak testing, the ECM opens the purge solenoid (Which is connected to engine vacuum) and closes the vent solenoid to seal the system
  • This pulls the system into vacuum, after a predetermined vacuum level is obtained by watching the FTP sensor, the ECM shuts off the purge solenoid sealing the vacuum in the system
  • The ECM then watches vacuum decay over time to determine if a leak is present.
  • If a predetermined vacuum level is not reached or vacuum decays to rapidly, a leak code will set.
  • If the system uses tank isolation for monitor logic, it will run multiple leak tests to isolate the location of the leak.

Basic Diagnostic Checks

  • Inspect for loose gas cap
  • Inspect hoses for cracks, leaks and proper routing and attachment
  • Check Key-on, Engine-off (KOEO) FTP sensor voltage for proper reading (See chart)
  • Check purge, vent and bypass solenoid function with scan tool or jumper wire (See Chart)
  • Check for mechanical leakage on all solenoids (See Chart)
  • If FTP sensor is in range, solenoids operate and no visual leaks are present, smoke/flow testing will be necessary for leak testing.
  • To prepare system for smoke/flow testing, use a scan tool or jumper wire to close vent solenoid and open bypass solenoid

GoTech Tips

Tip :Using a bypass solenoid and 2-way valve can eliminate tank vacuum during normal purging and help reduce fuel vaporization by keeping the tank in a slight pressure state


Tip :Because the bypass solenoid is normally closed and the 2-way valve holds pressure/vacuum in the tank, always check atmospheric FTP sensor readings with the fuel cap off and bypass sensor open