Evaporative System Integrity Monitor (ESIM) System


  • A Purge solenoid is used to purge fuel vapors and pull system into vacuum for leak detection
  • A EVAP Charcoal canister is used to absorb and store fuel vapors
  • A ESIM assembly is used to monitor the system for leaks
  • A Fuel Tank Pressure sensor is used for secondary component testing

System Leak Test Operation

  • The ESIM conducts tests on the evaporative system as follows: An engine off, non-intrusive test for small leaks and an engine running, intrusive test for medium/large leaks
  • To start the key off, non-intrusive testing, the engine control module (ECM) cycles the purge solenoid to equalize the system
  • The normally closed system will then naturally draw into a vacuum as the fuel and air in the system cool
  • After it reaches -1 In H20 the internal ESIM switch closes signaling the ECM the test passed
  • If the switch doesn't close in the allotted time, the ECM will log it as a leak test failure and run the intrusive medium/large leak test
  • The intrusive test still monitors the ESIM switch, except it uses the purge solenoid and manifold vacuum to pull the ESIM switch closed
  • The ECM then monitors how long it takes for the vacuum to decay and the switch to open up and compares to internal calculations to determine if a leak is present

Basic Diagnostic Checks

  • Inspect for loose Gas cap
  • Inspect hoses for cracks, leaks and proper routing and attachment
  • Check purge solenoid function with scan tool or jumper wires
  • Check purge solenoid for mechanical leakage
  • Check ESIM switch Circuits
  • Check ESIM internal switch with vacuum pump
  • If all checks pass, smoke/flow testing is required
  • Block EISM filter port to seal system for smoke/flow testing

GoTech Tips

Tip : ESIM mounting angle effects system calibration, ESIM and canister mounting angle must not be modified

Tip : It typically takes over a week for the small leak monitor to complete after repair
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