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, allow-
ing the PCM to monitor LDP pumping (diaphragm
up/down) activity. During the pumping mode, the dia-
phragm will not move down far enough to open the
vent valve. The pumping cycle is repeated as the sole-
noid is turned on and off. When the evaporative sys-
tem begins to pressurize, the pressure on the bottom
of the diaphragm will begin to oppose the spring pres-
sure, 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:
•
P0442 - EVAP LEAK MONITOR 0.040
9
LEAK
DETECTED
•
P0455 - EVAP LEAK MONITOR LARGE LEAK
DETECTED
•
P0456 - EVAP LEAK MONITOR 0.020
9
LEAK
DETECTED
•
P1486 - EVAP LEAK MON PINCHED HOSE
FOUND
•
P1494 - LEAK DETECTION PUMP SW OR MECH FAULT
•
P1495 - LEAK DETECTION PUMP SOLENOID CIRCUIT
25 - 16
EVAPORATIVE EMISSIONS
DR/DH