Emission System Integrity Monitor (ESIM)
| Refer to COMPONENT INDEX . |
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 12 volt signal to pass through the switch, pulling the signal low to ground. When the PCM sees the signal pulled low it determines the switch to be 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.
When installing an ESIM on the Charcoal Canister the O-ring can stick and roll causing a leak. To avoid this situation, talcum powder is recommended to lubricate the seal before installation. Also make sure that the ESIM is installed in the correct orientation with the connector at the 3 o'clock position so that the internal weights are in the correct position. Failure to do either of these could cause a failure and unnecessary replacement of the ESIM.