EVAP System Small Leak

Name of Code:
EVAP System Small Leak

When Monitored:
Immediately after a cold start, with ambient temperature between 40°F and 90°F and coolant temperature within 10°F of ambient temperature.

Set Condition:
If there is a leak larger than 0.040" and smaller than 0.080" in the evaporative system.


Theory of Operation:
The leak detection assembly incorporates two primary functions: it detects a leak in the evaporative system and seals the evaporative system so the leak detection test can be run.

The primary components within the assembly are a three-port leak detection solenoid that activates both of the functions described above, a pump containing a leak detection pump switch that monitors pump movement, two check valves and a spring diaphragm, and a canister vent valve seal containing a spring-loaded vent seal valve.

When the solenoid is energized, it allows engine vacuum to enter the pump and draw the diaphragm up, thus allowing atmospheric pressure to enter the pump cavity. When the solenoid is deenergized, it vents the engine vacuum thus permitting the spring to drive the diaphragm down, forcing air out of the pump cavity into the vent system. When the solenoid is energized and deenergized, the cycle is repeated, which creates flow in a typical diaphragm pump fashion.

After passing the leak detection phase of the test, system pressure is maintained until the purge system is activated, in effect creating a leak. If the cycle rate increases due to flow of the purge system, the test is passed and the diagnostic test is complete. If not, there is an obstruction in the system.

Possible Causes:
- A leak in the evaporative system between 0.040" and 0.080"
- Leak detection pump failure