Free ASE L1 (Advance Engine Performance) Prep from my smog repair class: Evaporative Canister Monitor:
BAR Specific Diagnostic Class:
The evaporative system is design to store and purge fuel vapors from the fuel system, and preventing them from escaping into the atmosphere.
The Evap system will deliver “HC” Hydrocarbons to the intake manifold above a preset speed to be burned by the engine as part of the normal air/fuel mixture.
The enable criteria has been met for one or two monitors to run so the “PCM” Power Train Control Module can test that particular circuit.
The Evaporative Canister Monitor could check for pressure, purging or a leak greater than .020” or .040” of an inch depending on the make model and year.
How does the Evap Monitor work
The “PCM” Power Train Control Module will turn on the Evap Vent Solenoid to block the fresh air supply to the Evap canister. At this point the purge solenoid will be turned on so the slight vacuum is created in the evap system.
Note: The Evap Vent Solenoid is located in the rear of the evap system while the Purge Solenoid is located in the front of the evap system.
There is a pressure sensor located in the gas tank that will indicate there is a vacuum in the system when the purge is turn on and the vent solenoid is blocked.
Then the Purge valve is turned off and the system is sealed to trap the vacuum in the evap system to check for leaks. The fuel tank pressure sensor signal is used to determine if evap system has any leaks.
The evap monitor has to determine if there is a 020” or .040” leak in the system. If the vacuum decays too rapidly a DTC and Freeze Frame will be stored in memory on the first trip and if the problem reoccurs on the second trip the “MIL” Malfunctioned Indicator Light will come indicating a problem.
However, if the same fault does not reoccur for 40 warm up cycles then the DTC and Freeze Frame will be erased from memory.
If the light is illuminated on the second trip and there is on reoccurring problem for three consecutive trips, the MIL will be extinguish.
Note: The evap monitor will only run if the gas level is between a ¼ of a tank of gas and ¾ of tank of gas.
The most common type of measurement for testing the Evap system is inches of water.
Chryslers uses a Leak Detection Pump that pressurizes the Evaporative system and seals the canister.
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