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ESIM on late model Chrysler vehicles

ESIM Evaporative Emissions System

Chrysler has used several different evaporative emissions testing systems over the years. Starting in 2007 Chrysler switched to the ESIM Evaporative Emission System. Prior to that, they use the Leak detection pump method from 1996-2004 and then the natural vacuum lead detection (NVLD) system from 2002-07.

All Evaporative test systems are designed to monitor the integrity of the hoses/tubes that run between the throttle body/intake and the fuel tank. Some car makers use engine vacuum to generate a negative pressure in the fuel system and then monitor that pressure to determine if there’s a leak, and if so, how big of a leak.

Chrysler uses a different system that relies on pressure changes as a liquid changes temperatures.

Chrysler Evaporative emissions components

Charcoal canister

Absorbs gasoline vapors during fill-up and chrysler evaprative canisterthe vapors are purged when the engine is running

ESIM (Evaporative System Integrity Monitor) switch

The ESIM switch acts like a vent valve used by other car makers, but also acts as a check valve—all without the need for a solenoid. The ESIM esim switchcontains two internal weights (small and large), a diaphragm and a switch. Because it uses weights, it relies on gravity to operate and must be installed in a vertical position. A rubber seal is attached at the end of each weight to act as a check valve. The large weight seals for pressure, while the small weight seals for vacuum.

Proportional purge valve

While other car makers use an open/closed solenoid, Chrysler uses a duty cycled proportional vapor canister purge valvepurge valve that opens and closes based on current applies.

The purge valve is normally closed (de-energized), so no gas vapors flow into the intake manifold in this state. The proportional purge solenoid is controlled by the PCM that senses the current being applied to the proportional purge solenoid and adjusts that current to achieve the desired purge flow. At a 50% duty cycle, voltage at the purge valve is approximately 6-v.

The proportional purge solenoid controls the purge rate of fuel vapors from the vapor canister and fuel tank to the engine intake manifold. During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid. The purge solenoid is located in the engine compartment at right rear next to the air box.

How the Chrysler ESIM switch works

During fill-up or when the tank is under pressure

During fill-up, vapor pressure from the tank pushes the heavier yellow weight off its seal and gas vapor flows into the charcoal canister. The pressure also pushes the diaphragm away from the electrical contacts. The ESIM contacts receives a reference voltage from the PCM and the PCM monitors voltage drop. When the system is under pressure and the diaphragm is pushed away, the contacts aren’t closed so the PCM sees no voltage drop.

When tank is under vacuum

When the fuel cools, the tank is under vacuum. esimThat vacuum pulls the light weight off its seat, allowing the tank to pull in air/vapor from the canister.

How the Chrysler EVAP System Test works

When the engine is off, both weights seal the tank from the charcoal canister. If the engine has been running, the fuel will be warm due to heat from the fuel pump. After shutdown the fuel cools and creates a vacuum. The same thing happens when ambient temperatures fall. The vacuum pulls the diaphragm towards the contacts, causing a switch closure. The PCM expects to see voltage drop from the closed contacts within a calculated time period and within a specified amount of key off events.

If the ESIM switch doesn’t close as per specs, the PCM runs an “intrusive” test during the next cold engine running sequence under the following conditions:

• engine coolant temperature must be within 50°F (10°C) of ambient temperature, indicating this is a cold start.
• fuel level must be between 12% and 88%.
• The engine must be in closed loop.
• Manifold vacuum must be greater than a minimum specified value.
• Ambient temperature must be between 39°F and 98°F (4°C and 37°C) and the elevation level must be below 8500 feet (2591 meters).

Purge monitor test

The purge monitor is a two stage test that tests the integrity of the hose attached between the purge valve and throttle body/intake. Stage one is non-intrusive—no switches are involved. The PCM commands the purge solenoid to flow at a specified rate to force the purge vapor ratio to update. The ratio is compared to a calibrated specification. If it is less than specified, a one trip failure is recorded. This test can detect if the purge hose is off, obstructed or the purge valve is not operational. The PCM monitors the flow rate by watching engine RPM and oxygen sensor readings. If the ratio is above a calibrated specification, the EVAP system passes. It fails the PCM runs stage two.

With the engine running, the PCM activates the purge solenoid to create a vacuum in the EVAP system. The PCM modulates the purge valve to create enough vacuum to pull the diaphragm closed and complete the circuit to ground. The PCM knows when that happens because it will see the voltage drop. It then closes the purge valve and clocks the length of time it takes for the vacuum to dissipate and the ESIM switch to open. If the switch opens quickly a large leak is recorded. If the switch opens after a predetermined amount of time, then the small leak matures.

If the switch doesn’t close during the test, a general evaporative failure is recorded.

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat

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