• 2020

Fault Finder


The ESIM (Evaporative System Integrity Monitor) is used for leak fault detection in the evaporative emissions (EVAP) system. The EVAP system is a closed system and it is necessary to its operation that it does not leak. The basic strategy used is that for leak testing is that in a sealed vessel, pressure will naturally increase or decrease in relation to temperature. Inside the ESIM, there is a switch that closes when the vacuum reaches a calibrated threshold. If the switch closes at this point, the system is not leaking (gasoline vapors are not being emitted to the atmosphere).

The ESIM is mounted directly to the charcoal canister (see Figure 1). On many vehicles, the ESIM is difficult to see and can be even more difficult to remove. This is not the case with the pictured vehicle, a 2013 Dodge Journey.

Figure 1


The evaporative emissions (EVAP) system is designed to manage gasoline vapors within the fuel system. A closed system prevents these vapors from escaping into the atmosphere. This is in stark contrast to the days of carburetors in which the fuel system was open. Gas tank caps were vented to the atmosphere, carburetors operated on the vacuum principle and the fuel storage system was a major source of hydrocarbon emissions. This is no longer the case.

This is how the EVAP system works. During refueling, liquid gasoline enters the fuel tank through the filler tube and displaces the fuel vapors in the fuel tank. These vapors escape the fuel tank through the fuel tank vent valves and are absorbed by a charcoal filter in the charcoal canister. When the engine enters closed loop operation, the purge solenoid will open, allowing engine vacuum from the intake manifold to draw fuel vapors from the charcoal canister into the intake manifold to be burned in the engine. The duty cycle/pulse width of the purge solenoid (in other words, the vapor flow rate) is controlled by PCM.

The ESIM is configured with a normally open vacuum switch and normally closed vacuum relief and pressure relief valves (see Figure 2). The relief valves regulate system pressure between 250Pa and -500Pa. The system is sealed whether there is vacuum or pressure unless it exceeds the regulation points. During purging, the vacuum relief valve is opened allowing fresh air to be drawn through the fresh air filter and charcoal canister to aid in drawing fuel vapors from the canister. The pressure relief valve limits any pressure build up in the fuel tank.

When the system vacuum reaches between -187Pa and -250Pa it acts on the diaphragm and closes the vacuum switch (see Figure 3). When the switch closes, it allows continuity between the terminals and the ESIM signal to pass through the switch, pulling the signal low to ground. The PCM monitors the signal to determine if the switch is open or closed (the signal can be between 5.0 volt and 12.0 volt). When the PCM reads voltage on the signal circuit it determines the switch is open and when the signal is pulled low, the switch is closed.

Figure 2


EVAP system problems are not likely to cause an engine performance problem that will be noticed by the driver; however, an EVAP problem will generate a Diagnostic Trouble Code (DTC). The four possible DTC’s are P0440 (General EVAP System Failure), P0452 (Pressure Switch Stuck Closed), P0455 (EVAP System Large Leak) and P0456 (EVAP System Small Leak). The most common faults we get are the leak faults (P0456 and P0455) and the purge performance fault (P0441).

Figure 3

Over time, the internal valves can become dirty preventing them from operating properly. The two valves can be clearly seen in Figure 2. If you were to shake a new ESIM before installing it, you can hear the valves rattle. To determine if the valve is stuck, perform the following simple test. Disconnect ESIM harness connector. If the switch state changes from closed to open, the ESIM is bad. It must be replaced.


Remove the spare tire. Raise and support the vehicle, then remove the fasteners and the spare tire well. Remove the fresh air hose from the port on the ESIM, and then disconnect the harness connector (see Figure 1). Be sure to clean the area around the ESIM harness before disconnecting it. This area is on the underside of the vehicle and it is dirty from road debris. Take care to prevent dirt from entering the connector.

There is a locking tab on the back of the ESIM unit (see Figure 2). Disengage the tab (pull it toward the ESIM body) while rotating the ESIM unit counter-clockwise 1/4 turn and remove it from the charcoal canister. Don’t forget to clean the area around the ESIM before removing it.

Before installing the new ESIM unit, be sure that the fresh air hose that attaches to it has a clear opening to the atmosphere. Check the fresh air hose, including the fresh air filter, for obstructions or restrictions at the ESIM. If a restriction is present, the system will not allow a free flow passage of clean air. This can result in an early shut off of the fuel fill nozzle during a fuel fill-up.

Be sure that the O-ring seal and the EVAP canister opening are clean. Install the O-ring seal into the groove on the charcoal canister. Be sure the O-ring seal (1) is fully seated in the groove of the canister (see Figure 4). The O-rings have a tendency to roll when installing the ESIM and can leak. You can lubricate the O-ring with talcum powder to help prevent this. Install the ESIM to the charcoal canister. Rotate the unit to engage the locking tab. After installing the ESIM, the harness connector must be in the 3 o’clock position. If the ESIM is not in this position, the switch will not operate properly. Next, install the fresh air hose and connect the harness connector to the ESIM (see Figure 3).

Figure 4

Install the spare tire well and securely tighten the fasteners. Install the spare tire, remove the support and lower the vehicle.

In order to verify that the new ESIM is working properly, perform a leak check on the EVAP system. Using the EELD Kit and accessory 8404C, set it to the air setting. Verify that the ball in the flow meter drops and stays at the bottom of the flow meter.

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