Chrysler's ESIM Detects Leaks in Evaporative SystemPosted 2/4/2008
By Arlen Mauland
The Evaporative System Integrity Monitor (ESIM) is the latest Chrysler system for detecting leaks in the evaporative system. It is similar to the Natural Vacuum Leak Detection (NVLD) system, which uses the ideal gas law to detect leaks in the fuel tank, canister and hoses. The fuel tank, canister and hoses form a sealed system. When the engine has been running, the temperature of the fuel in the fuel tank is raised slightly. When the engine is shut off, the temperature of the fuel should drop. The ideal gas law states that in a sealed system the pressure drops proportionately to a drop in temperature. The powertrain control module (PCM) monitors a vacuum switch that is built into the ESIM. The slight drop in pressure is detected by this switch. If the PCM does not see the switch change state after an engine shutdown, it assumes there is a leak in the sealed system (fuel tank, canister and hoses).
Small leaks are detected when the engine is shut off. The first 10 minutes after the engine is shut off, the state of the vacuum switch is ignored by the PCM. The PCM briefly energizes the purge valve to act as a vent. After 10 minutes, the PCM starts looking for the expected closure of the vacuum switch. The temperature of the fuel only needs to drop about 3 degrees Fahrenheit for the pressure to drop enough to close the switch. The PCM monitors the vacuum switch for up to 1,050 minutes after the engine is shut off. If the switch closes anytime within 10 to 1,050 minutes after the engine is shut off, the PCM registers a "small leak pass." If the vacuum switch does not close in this time, the key off time without a switch closure is added to the total accumulated key off time without a switch closure. When the total accumulated key off time without a switch closure reaches 4,200 minutes, the PCM records a fault for a small leak.
There are two weighted check valves in the ESIM. Therefore, the ESIM must be mounted in a vertical position for the weighted check valves to work properly. These weighted check valves prevent excessive pressure or vacuum in the system.
This is just a brief overview of the ESIM system. If you have further questions, please give us a call.
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