Theory Of Operation
The Evaporative Leak Check Module (ELCM) is used to perform the required on board Evaporative System Leak Test. The ELCM contains several different components that are used during testing. The Powertrain Control Module (PCM) controls the operation of these components. A list of the internal components and functions include:
- Vacuum Pump - Used during the engine off leak testing to lower the system pressure to a vacuum for leak testing.
- 0.20" Reference Orifice - Simulates a small leak to determine a pass/fail threshold to measure the system against during the engine off leak testing.
- Change-Over Valve (Spring loaded, normally closed) - Closes the system off when de-energized and allows ambient air to be drawn in through the 0.20" Reference Orifice and measured during the phase 1 orifice check to determine a small leak pass/fail threshold. The Change-Over Valve is energized during leak testing to close off the passage to the ambient air and open to the Evaporative System for leak testing diagnostics to be performed.
- Absolute Pressure Sensor - Measures the pressure/vacuum reading through the orifice during the 0.20" Reference Orifice check and measures the pressure/vacuum reading of the Evaporative System during leak testing. These two values are compared to determine if a leak is present in the system.