Grand Cherokee 2WD Limited V8-4.7L (2002)
Fig. 15 Diaphragm Downward Movement
Diaphragm Downward Movement
Based on reed switch input, the PCM de-energizes the LDP solenoid, causing it to block the vacuum port, and open the atmospheric port. This
connects the upper pump cavity to atmosphere through the EVAP air filter. The spring is now able to push the diaphragm down. The downward
movement of the diaphragm closes the inlet check valve and opens the outlet check valve pumping air into the evaporative system. The LDP reed
switch turns from open to closed, allowing the PCM to monitor LDP pumping (diaphragm up/down) activity. During the pumping mode, the
diaphragm will not move down far enough to open the vent valve. The pumping cycle is repeated as the solenoid is turned ON and OFF. When the
evaporative system begins to pressurize, the pressure on the bottom of the diaphragm will begin to oppose the spring pressure, slowing the pumping
action. The PCM watches the time from when the solenoid is de-energized, until the diaphragm drops down far enough for the reed switch to change
from opened to closed. If the reed switch changes too quickly, a leak may be indicated. The longer it takes the reed switch to change state, the tighter
the evaporative system is sealed. If the system pressurizes too quickly, a restriction somewhere in the EVAP system may be indicated.
Pumping Action
Action : During portions of this test, the PCM uses the reed switch to monitor diaphragm movement. The solenoid is only turned ON by the PCM after
the reed switch changes from open to closed, indicating that the diaphragm has moved down. At other times during the test, the PCM will rapidly
cycle the LDP solenoid ON and OFF to quickly pressurize the system. During rapid cycling, the diaphragm will not move enough to change the reed
switch state. In the state of rapid cycling, the PCM will use a fixed time interval to cycle the solenoid. If the system does not pass the EVAP Leak
Detection Test, the following DTCs may be set:
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P0442 - EVAP LEAK MONITOR 0.040" LEAK DETECTED
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P0455 - EVAP LEAK MONITOR LARGE LEAK DETECTED
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P0456 - EVAP LEAK MONITOR 0.020" LEAK DETECTED
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P1486 - EVAP LEAK MON PINCHED HOSE FOUND
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P1494 - LEAK DETECTION PUMP SW OR MECH FAULT
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P1495 - LEAK DETECTION PUMP SOLENOID CIRCUIT
