Evaporative System Leak Detection Monitor (If Equipped)

The Evaporative System Integrity Monitor (ESIM) is the next generation evaporative leak detection system that is used on vehicles equipped with either the Next Generation Controller (NGC) or Global Powertrain Engine Controller (GPEC). The operation of this monitor is similar to the Natural Vacuum Leal Detection (NVLD) system it replaces. A leak detection pump is no longer required and the system is able to detect a leak equivalent to a 0.020" (0.5 mm) hole.

The basic leak detection theory employed with ESIM is the "Gas Law". This is to say that the pressure in a sealed vessel will change if the temperature of the gas in the vessel changes. The vessel will only see this effect if it is indeed sealed. Even small leaks will allow the pressure in the vessel to come to equilibrium with the ambient pressure. In addition to the detection of very small leaks, this system has the capability of detecting medium as well as large evaporative system leaks.

The ESIM seals the canister vent during engine off conditions. If the EVAP system has a leak of less than the failure threshold, the evaporative system will be pulled into a vacuum, either due to the cool down from operating temperature or diurnal ambient temperature cycling. The diurnal effect is considered one of the primary contributors to the leak determination by this diagnostic. When the vacuum in the system exceeds about 1" H2O (0.25 KPA), a vacuum switch closes. The switch closure sends a signal to the powertrain module. The module, via appropriate logic strategies, utilizes the switch signal, or lack thereof, to make a determination of whether a leak is present.