Dakota, 2001-2005

Leak Detection Pump

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NOTE
On 2003 & later 4.7L engines, see NATURAL VACUUM LEAK DETECTION (NVLD).

Description & Operation



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 40F and 86F, 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.

Removal & Installation



The LDP is located in the engine compartment under the battery tray and Power Distribution Center (PDC). The LDP filter is attached to the outside of battery tray. The LDP and LDP filter are replaced (serviced) as one unit.

  1. Disconnect negative battery cable at battery.
  2.  
  3. Remove battery.
  4.  
  5. Carefully disconnect rubber hose from bottom of LDP filter.
  6.  
  7. Remove clip retaining LDP filter to battery tray and remove filter from tray.
  8.  
  9. Disconnect battery temperature sensor pigtail wiring harness at bottom of battery tray.
  10.  
  11. To gain access to LDP, the PDC must be partially removed. Remove PDC-to-fender mounting screw at rear of PDC. Unsnap PDC from battery tray.
  12.  
  13. To prevent damage to PDC wiring, carefully position PDC to gain access to LDP.
  14.  
  15. Remove battery tray.
  16.  
  17. Carefully remove vapor/vacuum lines at LDP.
  18.  
  19. Disconnect electrical connector at LDP.
  20.  
  21. Remove 3 LDP mounting screws and remove LDP from vehicle.
  22.  

To Install:

  1. Install LDP to bottom of battery tray. Tighten screws to 1 Nm (11 inch lbs..) torque.
  2.  
  3. Carefully install vapor/vacuum lines to LDP.
    WARNING
    The vapor/vacuum lines and hoses must be firmly connected. Check the vapor/vacuum lines at the LDP. LDP filter and EVAP canister purge solenoid for damage or leaks. If a leak is present, a Diagnostic Trouble Code (DTC) may be set.

  4.  
  5. Connect electrical connector to LDP.
  6.  
  7. Install battery tray.
  8.  
  9. Install PDC to fender and battery tray (snaps on to battery tray).
  10.  
  11. Install LDP filter to battery tray (one clip).
  12.  
  13. Install connecting hose to bottom of LDP filter.
  14.  
  15. Connect battery temperature sensor pigtail wiring harness.
  16.  
  17. Install battery.
  18.  
  19. Connect negative battery cable to battery.
  20.  

 
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