Neon, 2000-2005

Leak Detection Pump

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Description & Operation



The evaporative emission system is designed to prevent the escape of fuel vapors from the fuel system. Leaks in the system, even small ones, can allow fuel vapors to escape into the atmosphere. Government regulations require on-board Testing to make sure that the evaporative (EVAP) system is functioning properly. The leak detection system tests for EVAP system leaks and blockage. It also performs self-diagnostics.

During self-diagnostics, the Powertrain Control Module (PCM) first checks the Leak Detection Pump (LDP) for electrical and mechanical faults. If the first checks pass, the PCM then uses the LDP to seal the vent valve and pump air into the system to pressurize it. If a leak is present, the PCM will continue pumping the LDP to replace the air that leaks out. The PCM determines the size of the leak based on how fast/long it must pump the LDP as it tries to maintain pressure in the system.

EVAP Leak Detection System Components

Service Port: Used with special tools like the Miller Evaporative Emissions Leak Detector (EELD) to test for leaks in the system.

EVAP Purge Solenoid: The PCM uses the EVAP purge solenoid to control purging of excess fuel vapors stored in the EVAP canister. It remains closed during leak Testing to prevent loss of pressure.

EVAP Canister: The EVAP canister stores fuel vapors from the fuel tank for purging. EVAP Purge Orifice: Limits purge volume.

EVAP System Air Filter: Provides air to the LDP for pressurizing the system. It filters out dirt while allowing a vent to atmosphere for the EVAP system.

The main purpose of the LDP is to pressurize the fuel system for leak checking. It closes the EVAP system vent to atmospheric pressure so the system can be pressurized for leak Testing. The diaphragm is powered by engine vacuum. It pumps air into the EVAP system to develop a pressure of about 7.5 H2O (1/4) psi. A reed switch in the LDP allows the PCM to monitor the position of the LDP diaphragm. The PCM uses the reed switch input to monitor how fast the LDP is pumping air into the EVAP system. This allows detection of leaks and blockage.

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Fig.

Removal & Installation



  1. Raise and support vehicle on a hoist.
  2.  
  3. Push locking tab on electrical connector to unlock and remove connector.
  4.  
  5. Loosen the sway bar bracket to remove the pump bracket.
  6.  
  7. Remove pump and bracket as an assembly.
  8.  
  9. Disconnect lines from LDP.
  10.  
  11. Remove filter. Remove pump from bracket.
  12.  

To Install:

  1. Install pump to bracket and tighten bolts to 1.2 Nm (10.6 inch lbs.).
  2.  
  3. Install filter and tighten to 2.8 Nm (25 inch lbs.).
  4.  
  5. Before installing hoses to LDP, make sure they are not cracked or split. If a hose leaks, it will cause the Check Engine Lamp to illuminate. Connect lines to the LDP.
    NOTE
    The LDP bracket must be between the rail and sway bar bracket.

  6.  
  7. Install pump and bracket assembly to body and tighten bolts to 5.0 Nm (45 inch lbs.).
  8.  
  9. Install sway bar bracket bolt and tighten bolts to 33.8 Nm (25 ft. lbs.).
  10.  
  11. Install electrical connector to pump and push locking tab to lock.
  12.  
  13. Use the scan tool, verify proper operation of LDP.
  14.  

Testing



Enabling Conditions To Run EVAP Leak Detection Test

NOTE
The following values are approximate and vehicle specific. Use the values seen in pretest/monitor test screen on the DRB III or suitable scan tool. See TSB 25-02-98 for more detail.



Cold start: with ambient temperature (obtained from modeling the inlet air temperature sensor on passenger vehicles and the battery temperature sensor on Jeep & truck vehicles) between 4C(40F) and 32C (90F) for 0.040 leak. Between 4C(40F) and 29C (85F) for 0.020 leak.
 
Engine coolant temperature within: -12to -8C (10to 18F) of battery/ambient.
 
Battery voltage between 10 and 15 volts.
 


NOTE
If battery voltage drops below 10 volts for more than 5 seconds during engine cranking, the EVAP leak detection test will not run.



Low fuel warning light off (fuel level must be between 15% and 85% for 0.040 leak and 30% and 85% for 0.020 leak).
 
MAP sensor reading 22 in Hg or above (This is the manifold absolute pressure, not vacuum).
 

No Engine Stall During Test

If the system does not pass the EVAP Leak Detection Test, the following DTCs may be set:



P0442 - EVAP LEAK MONITOR 0.040 LEAK DETECTED
 
P0455 - EVAP LEAK MONITOR LARGE LEAK DETECTED
 
P0456 - EVAP LEAK MONITOR 0.020 LEAK DETECTED
 
P1486 - EVAP LEAK MON PINCHED HOSE FOUND
 
P1494 - LEAK DETECTION PUMP SW OR MECH FAULT
 
P1495 - LEAK DETECTION PUMP SOLENOID CIRCUIT
 

A DTC will not be set if a one-trip fault is set or if MIL is illuminated for any of the following:



Purge Solenoid Electrical Fault
 
All Engine Controller Self Test Faults
 
All Cam and/or Crank Sensor Fault
 
All Map Sensor Faults
 
Ambient/battery Temperature Sensor Electrical Faults
 
All Coolant Sensor Faults
 
All TPS Faults
 
LDP Pressure Switch Fault
 
EGR Solenoid Fault
 
All Injector Faults
 
BARO Out Of Range
 
Vehicle Speed Faults
 
LDP Solenoid Circuit
 

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.

 
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