Durango 4WD V8-5.9L VIN Z (1998)
Figure 6
EVAP leak detection test sequence
When the ignition key is turned to "ON" the LDP diaphragm should be in the down position and the LDP reed switch should be closed. If the EVAP
system has residual pressure, the LDP diaphragm may be up. This could result in the LDP reed switch being open when the key is turned to "ON" and a
P1494 fault could be set because the PCM is expecting the reed switch to be closed.
After the key is turned "ON", the PCM immediately tests the LDP solenoid circuit for electrical faults. If a fault is detected, DTC P1495 will set, the
MIL will illuminate, and the remaining EVAP Leak Detection Test is canceled.
NOTE: If battery temperature is not within range, or if the engine coolant temperature is not within a specified range of the battery temperature, the
PCM will not run tests for DTC P1494, P1486, P0442, P0455 and P0441. These temperature calibrations may be different between models.
FIGURE 6 SECTION 2
If DTC P1495 is not set, the PCM will check for DTC P1494. If the LDP reed switch was closed when the key was turned to "ON", the PCM energizes
the LDP solenoid for up to 8 seconds and monitors the LDP switch. As the LDP diaphragm is pulled up by engine vacuum, the LDP reed switch should
change from closed to open. If it does not, the PCM sets a temporary fault (P1494) in memory, and waits until the next time the Enabling Conditions are
met to run the test again. If this is again detected, P1494 is stored and the MIL is illuminated. If the problem is not detected during the next enabling
cycle, the temporary fault will be cleared.
However, if the PCM detects the reed switch open when the key is turned to "ON", the PCM must determine if this condition is due to residual pressure
in the EVAP system, or an actual fault. The PCM stores information in memory on EVAP system purging from previous engine run or drive cycles.
If little or no purging took place, residual pressure could be holding the LDP diaphragm up, causing the LDP switch to be open. Since this is not a
malfunction, the PCM cancels the EVAP Leak Detection Test without setting the temporary fault.
If there was sufficient purging during the previous cycle to eliminate EVAP system pressure, the PCM judges that this is a malfunction and sets a
temporary fault in memory. The next time that the Enabling Conditions are met, the test will run again. If the fault is again detected, the MIL will
