by Benjamin may chi
(Los angels CA )
The LDP . Leak detection pump has many components assembled in one housing, some of the components are, reed switch, pressure vacuum solenoid, pump diaphragm, one way valve , and various ports for vacuum and air. .LDP does not have an electric vent valve or tank pressure sensor. The control side of the LDP is at the upper part of the diaphragm, and the ultimate goal which is pumping air into the canister takes place at the bottom part of the LDP, something like a relay that has control side and a current flow side ,in this case we have air flow side. . The pcm monitors the system using the reed valve switch that is lifted up by the vacuum , when the solenoid is activated it opens the vacuum port and as it moves more it closes the fresh air port the pcm activates the solenoid using the duty cycle method, this cause the diaphragm to mover up and down and as goes down it squeezes air into the canister port, as the pressure buildup the pump slows down eventually stops, the pcm then monitors the length of time the diaphragm takes to drop that will cause the reed valve to send a 12 volt signal to the pcm if the valve closes to soon the pcm will store a code indicating a leak
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