Emission System Integrity Monitor (ESIM)
WARNING: This page is about a different variant/trim than selected.
The ESIM is configured with a normally open vacuum switch and normally closed vacuum relief and pressure relief valves (see figure above). The PCM uses the ESIM for all system leak diagnostics (P0440, P0455 and P0456). The relief valves regulate the system pressure between approximately 250Pa and -500Pa.
- When the system vacuum reaches between (-187Pa) and (-250Pa) it acts on the diaphragm and closes the vacuum switch. When the switch closes it allows continuity between the terminals. This allows the ESIM Signal to pass through the switch, pulling the signal low to ground. The PCM monitors the signal to determine the state of the switch (open or closed). The ESIM Signal can be a 5.0 volt or 12.0 volt signal depending on the vehicle . When the PCM reads voltage on the signal circuit it determines the switch is open and when the signal is pulled low the PCM determines the switch is closed.
- The vacuum relief valve is intended to maintain the seal on the system during engine off events. However if the vacuum exceeds the regulation point the valve will pull off the seat to protect the system from excessive vacuum conditions. During purging, the vacuum relief valve inside, the ESIM is opened allowing fresh air to be drawn through the fresh air filter and Charcoal Canister to aid in drawing the fuel vapor from the canister.
- The pressure relief valve limits any pressure build up in the Fuel Tank during refueling and allows the tank pressure to normalize during increasing temperature events. This is additionally beneficial because it achieves a switch closed state (pass threshold) sooner than if the tank has to decay from a much higher pressure.