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Hello and welcome to just answer Jeep. Your Jeep uses an Evaporative emission system Leak Detection Pump (LDP). All vehicles built since 1996 employ some type of leak detection system. This code means that the PCM (engine computer) sees a problem with the pump or circuit. This is usually caused by a bad pump, but can also be set if there is no vacuum to the pump. I recommend first checking to see if there is vacuum at the hose connected to the pump. If there is then replace the LDP.
Here is some information from the service manual for you to read. Hope this helps and let me know if you need further assistance with this.
The Leak Detection Pump (LDP) is used only with certain emission packages.
The LDP is a device used to detect a leak in the evaporative system.
The pump contains a 3 port solenoid, a pump that contains a switch, a spring loaded canister vent valve seal, 2 check valves and a spring/diaphragm.
Immediately after a cold start, engine temperature between 40°F and 86°F, the 3 port solenoid is briefly energized. This initializes the pump by drawing air into the pump cavity and also closes the vent seal. During non-test test conditions, the vent seal is held open by the pump diaphragm assembly which pushes it open at the full travel position. The vent seal will remain closed while the pump is cycling. This is due to the operation of the 3 port solenoid which prevents the diaphragm assembly from reaching full travel. After the brief initialization period, the solenoid is de-energized, allowing atmospheric pressure to enter the pump cavity. This permits the spring to drive the diaphragm which forces air out of the pump cavity and into the vent system. When the solenoid is energized and de-energized, the cycle is repeated creating flow in typical diaphragm pump fashion. The pump is controlled in 2 modes:
PUMP MODE: The pump is cycled at a fixed rate to achieve a rapid pressure build in order to shorten the overall test time.
TEST MODE: The solenoid is energized with a fixed duration pulse. Subsequent fixed pulses occur when the diaphragm reaches the switch closure point.
The spring in the pump is set so that the system will achieve an equalized pressure of about 7.5 inches of water.
When the pump starts, the cycle rate is quite high. As the system becomes pressurized pump rate drops. If there is no leak the pump will quit. If there is a leak, the test is terminated at the end of the test mode.
If there is no leak, the purge monitor is run. If the cycle rate increases due to the flow through the purge system, the test is passed and the diagnostic is complete.
The canister vent valve will unseal the system after completion of the test sequence as the pump diaphragm assembly moves to the full travel position.
The LDP is located in the right-rear side of engine compartment EVAP Canister Purge Solenoid (With LDP) The LDP filter is located above the LDP EVAP Canister Purge Solenoid (With LDP) The LDP and LDP filter are replaced (serviced) as one unit.
P-1494 LEAK DETECT PUMP SW OR MECHANICAL FAULT
When Monitored and Set Condition:
When Monitored: Immediately after a cold start, with battery/ambient temperature
between 40 deg. F and 90 deg. F and coolant temperature within 10 deg. F of battery/
Set Condition: The state of the switch does not change when the solenoid is energized.
WIRING HARNESS INTERMITTENT
LDP SWITCH SENSE CIRCUIT OPEN
LDP SWITCH SENSE CIRCUIT SHORTED TO GROUND
LEAK DETECTION PUMP
POWERTRAIN CONTROL MODULE
TEST ACTION APPLICABILITY
1 Ignition On, Engine Not Running.
With the DRB, read the DTC's.
Is the DTC specific good trip counter displayed and equal to zero for P1494?
Yes ® Go To 7
No ® Go To 2
2 Determine if the DTC matches FREEZE FRAME DTC.
Is DTC equal to FREEZE FRAME DTC?
Yes ® Go To 3
No ® Repair the DTC with FREEZE FRAME data.
Perform Powertrain Verification Test VER-6.
3 Engine Running.
With DRB, perform the Leak Detect Pump Test, press up or down arrow for switch
While monitoring the LDP switch state, wiggle Wiring Harness from the LDP
Solenoid to the PCM.
Did the LDP switch state ever stop toggling?
Yes ® Repair as necessary where wiggling caused problem to appear.
No ® Go To 4
4 Ignition Off
Using the schematic as a guide, inspect the Wiring and Connectors.
Were any problems found?
Yes ® Repair as necessary
No ® Go To 5
5 Read the Freeze Frame Data.
Try to duplicate the conditions in Freeze Frame. Pay particular attention to the DTC
setting conditions such as, speed, temp and load.
Did the DTC specific good trips change to 0?
Yes ® Go To 6
No ® Test Complete.
6 Start engine and let idle.
Note: LDP Switch should be closed at start of test.
With the DRB, perform the Leak Detect Pump Test.
Observe LDP Switch state.
Press 1 to pump.
Read the LDP Pump Switch state.
Did the LDP Switch State toggle?
Yes ® Test Complete.
No ® Go To 7
7 Ignition Off
Disconnect the Engine Vacuum Supply Hose at the Leak Detection Pump.
Install a Vacuum gauge to Engine Vacuum Supply Hose at the Leak Detection Pump.
Start the engine and read Vacuum Gauge.
Does Vacuum Gauge read within 1 inch of engine vacuum?
Yes ® Go To 8
No ® Repair the leak or obstruction in Vacuum Hose.
8 Turn ignition off.
Disconnect the Leak Detection Pump electrical connector.
Turn ignition on.
With the DRB in Inputs/Outputs, read the "Leak Detect Pump Sw" state.
While observing the "Leak Detect Pump Sw" state, connect a jumper wire between
the Fused Ignition Switch Output circuit and the LDP Switch Sense circuit.
Did the "Leak Detect Pump Sw" state change when the jumper was connected?
Yes ® Replace the Leak Detection Pump.
No ® Go To 9
P-1494 LEAK DETECT PUMP SW OR MECHANICAL FAULT - Continued
9 Ignition Off.
Disconnect the Leak Detection Pump Connector.
Note: Check connectors - Clean/repair as necessary.
Disconnect the PCM connectors.
Using an Ohmmeter, measure the resistance of the LDP Switch Sense Circuit from
the PCM Connector to LDP Connector.
Is the resistance below 5.0 ohms?
Yes ® Go To 10
No ® Repair open Leak Detection Pump Switch Sense Circuit.
10 Ignition Off.
Using an Ohmmeter, measure the resistance between the LDP Switch Sense Circuit
Yes ® Repair LDP Pressure Switch Circuit for a short to ground.
No ® Go To 11
11 If there are no potential causes remaining, view repair options. All