Theory Of Operation
OVERVIEW: The Evaporative Non-Integrated Leak Monitor (ENILM) diagnostics are performed in the engine off (after run) state. The diagnostic will run after the ignition is off for 6 hours. The reason for the wait time is that there are cases where the Fuel Tank pressure increases greatly after ignition off (due to high temperatures) and is too large for the ELCM Vacuum Pump to create vacuum. This could cause a false failure during small leak testing. After the calibrated wait time the Powertrain Control Module (PCM) will initiate the Evaporative System Small Leak diagnostic. The Evaporative Leak Check Module (ELCM) and Fuel Tank Isolation Valve (FTIV) are key components used in diagnosing the system. Refer to the Description and Operation of the ELCM and FTIV for more specific details on how the components function for diagnostics.
The Evaporative system should not be tested by putting smoke into the system because the residue from the smoke being generated will damage the ELCM.
DIAGNOSTICS: The ENILM system used on the PHEV vehicles is divided into two parts at the FTIV (review figure below), the Fuel Tank side and Fresh Air side . The two sides of the system are diagnosed for leaks independent of each other by the PCM. However, if the Fresh Air side of the system is determined to be leaking, the FTIV is opened and the entire system is checked for a leak. Because of this a leak on the Fresh Air side will typically set a leak fault against both the Fresh Air and Fuel Tank sides, whereas a leak on the Fuel Tank side should only set a leak fault against the Fuel Tank side. One exception to this could be a small leak internally through the FTIV. This condition could cause the Fresh Air side to fail leak testing and set a fault but pass leak test of the entire system and therefore not set a Fuel Tank side leak. In most cases the FTIV Stuck Open DTC (P2450) should also be set but may not if the leak is small.
It is important to note when manually leak testing a system that extreme high or low temperatures during leak testing can yield poor results and a false failure or passing of the system. For best results, if one of the previous conditions is true, allow the vehicle to sit inside the shop and achieve a reasonable temperature before checking for leaks. Recommend somewhere between approximately 10°C (50°F) and 30°C (86°F).
LEAK TESTING: If the ambient and fuel temperatures are not excessive the system can be checked for a leak using the Evaporative Emissions Leak Detection (EELD) Tester. The Fresh Air side of the system should never be tested by putting smoke into the system because the residue from the smoke being generated will damage the ELCM. It is also recommended not to use smoke to find a leak on the Fuel Tank side of the system since any residual smoke lingering in the system could make drawn through the ELCM when the PCM performs the subsequent leak testing. Also important to note during testing is that the ELCM is vented to atmosphere when the Change-Over Valve (COV) inside the ELCM is de-energized (off).
- The best way to check the Fresh Air side for a leak is to disconnect the line at the ELCM, connect the EELD Tester, and Air test the system to verify a leak is present. If a leak is present, the EELD Tester can be moved to other points in the system and retested. This could help narrow down the leak to a particular component that is leaking. If it is determined that the leak is not one of the components, pressurizing the system using the EELD Tester and checking the lines and connections with Mopar Air Leak Detector can be an effective way to find an external leak.
- Likewise, when checking the Fuel Tank side for a leak it is best to connect the EELD Tester and Air test the system to verify a leak is present. If a leak is present, pressurize the system using the EELD Tester and check the lines and connection points with Mopar Air Leak Detector to check for leaks.