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Leak Detection Pump (LDP) pressure switch problem - the solenoid circuit

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  • aikiden May 06, 2009

    Engine warning light is on. At first heard this loud whistling noise coming from the fuel tank but that stopped after about 2 weeks. Diagnostic code is P1494 which is "Leak Detection Pump Software or Mechanical fault" 

  • yadayada
    yadayada May 11, 2010

    Are you talking about the evap system?

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3.3l engine. What are the probable causes of DTC P1495?


answer courtesy of engine codes .com Engine-Codes OBDII Code List P1495 Dodge
P1495 Dodge P1495 Dodge - EVAP Leak Detection Pump Solenoid Circuit Condition 3 ' Add Comment Possible causes
- Faulty Leak Detection Pump (LDP)
- Leak Detection Pump (LDP) harness is open or shorted
- Leak Detection Pump (LDP) poor electrical connection
What does this mean? When is the code detected?
Malfunction is detected when the Powertrain Control Module (PCM) detected the pump solenoid did not change status when activated,
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- Possible a noticeable fuel odor caused by the release of fuel vapors
P1495 Dodge Description
The Evaporative emissions system is design to prevent the escape of fuel vapors from the fuel system. Leaks in the system, ca allow vapors to escape into the atmosphere. The leak detection system tests for EVAP system leaks and blockage.
During the 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.

Read more: http://engine-codes.com/p1495_dodge.html#ixzz3iQ8P3JII P1495 Dodge EVAP Leak Detection Pump Solenoid Circuit Condition

Aug 10, 2015 | Dodge Caravan Cars & Trucks

1 Answer

P1495 on 2000 dodge stratus 2.4 l engine how to fix the problem


The code is telling you that you have a problem with the pump.

DTC P1495 - LEAK DETECTION PUMP SOLENOID CIRCUIT
WHEN MONITORED Ignition on and battery voltage greater than 10.4 volts .
SET CONDITION The state of the solenoid circuit does not change.
POSSIBLE CAUSES Fused ignition switch output circuit open
Leak detection pump defective LDP solenoid circuit wiring harness observable def LDP solenoid ckt wiring harness intermittent def LDP solenoid control circuit short to ground Leak detection pump solenoid control circuit open Powertrain control module defective

During evaporative system diagnosis, Leak Detection Pumps have mistakenly been replaced. A thorough inspection for pinched, kinked, or disconnected supply vacuum lines (as currently listed in the Powertrain Diagnostic Procedures) is a critical step in diagnosing DTC P1494 (LDP SW OR MECHANICAL FAULT). Additionally, the other evaporative leak faults (DTC P0442 - SMALL LEAK, P0455 - LARGE LEAK, and P0456 - VERY SMALL LEAK) should have the supply vacuum lines examined for pinches or kinks prior to any LDP component replacement.



The supply vacuum lines should be checked from the engine compartment all the way to the fuel tank, including the LDP and purge system.

NOTE: VERIFY ALL RELATED SUPPLY VACUUM LINE ROUTINGS FOR PINCHES, KINKS, OR DISCONNECTION'S BEFORE REPLACING LDP SYSTEM COMPONENTS.




Hope this helps, also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Apr 16, 2012 | Cars & Trucks

1 Answer

2000 dodge stratus p1495 code problem


Check your connections on your leak detection pump and vacuum hose to the engine. You will need a scanner to do a wiggle test on the wiring harness this is a common problem.

The code is telling you that you have a problem with the pump.

DTC P1495 - LEAK DETECTION PUMP SOLENOID CIRCUIT
WHEN MONITORED Ignition on and battery voltage greater than 10.4 volts .
SET CONDITION The state of the solenoid circuit does not change.

POSSIBLE CAUSES: Fused ignition switch output circuit open
Leak detection pump defective LDP solenoid circuit wiring harness observable def LDP solenoid ckt wiring harness intermittent def LDP solenoid control circuit short to ground Leak detection pump solenoid control circuit open Powertrain control module defective

Hope helps.

Apr 16, 2012 | Cars & Trucks

1 Answer

Code p1494. what do i look for.


P1494 (M)Leak Detection Pump Sw or Mechanical Fault. Incorrect input state detected for the Leak Detection Pump (LDP) pressure switch.

The Evaporative LDP switch may be bad or the pump itself has a problem. Check the pump, the wire connections, and the hoses attached to it.





LEAK DETECTION PUMP (LDP)
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 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. 180562d1295135687t-diagnostic-code-p1494-evap-wldp.jpg

Jan 19, 2011 | 1997 Jeep Grand Cherokee

1 Answer

Check engine light is on and when checked it pulls a malfunction code (code P1494) leak detection switch or mechanical failure. Is it still under warranty under the emissions? It is a 2001 Jeep Grand...


First off, a model year 2001, its possible still covered under the 5 year/50,000 mile emissions warranty. That's federal law. So you should not have had to pay a penny for that repair since the Leak Detection Pump is an emission control device.

As is the Charcoal Canister. If that is bad there should be no charge for repair or replacement. I hope you saved the receipts because I think they owe you a bunch of money. If they give you an argument about it, call Chrysler and they will take care of it.

Now, are you ready to learn more about the Leak Detection Pump then you will ever need to know? Good! Here it is!

Leak Detection Pump (LDP) Operation And Diagnosis:
* 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 Monitor Pinched Hose Found
* P1494-Leak Detection Pump SW Or Mechanical Fault
* P1495-Leak Detection Pump Solenoid Circuit

Introduction:
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 (remember I said that?) 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.

Leak Detection Pump (LDP) Components:
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' H20(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.

The LDP assembly consists of several parts. The solenoid is controlled by the PCM, and it connects the upper pump cavity to either engine vacuum or atmospheric pressure. A vent valve closes the EVAP system to atmosphere, sealing the system during leak testing. The pump section of the LDP consists of a diaphragm that moves up and down to bring air in through the air filter and inlet check valve, and pump it out through an outlet check valve into the EVAP system.

The diaphragm is pulled up by engine vacuum, and pushed down by spring pressure, as the LDP solenoid turns on and off. The LDP also has a magnetic reed switch to signal diaphragm position to the PCM. When the diaphragm is down, the switch is closed, which sends a 12 V (system voltage) signal to the PCM. When the diaphragm is up, the switch is open, and there is no voltage sent to the PCM. This allows the PCM to monitor LDP pumping action as it turns the LDP solenoid on and off.

LDP At Rest (Not Powered):
When the LDP is at rest (no electrical/vacuum) the diaphragm is allowed to drop down if the internal (EVAP system) pressure is not greater than the return spring. The LDP solenoid blocks the engine vacuum port and opens the atmospheric pressure port connected through the EVAP system air filter. The vent valve is held open by the diaphragm. This allows the canister to see atmospheric pressure.

Diaphragm Upward Movement:
When the PCM energizes the LDP solenoid, the solenoid blocks the atmospheric port leading through the EVAP air filter and at the same time opens the engine vacuum port to the pump cavity above the diaphragm. The diaphragm moves upward when vacuum above the diaphragm exceeds spring force. This upward movement closes the vent valve. It also causes low pressure below the diaphragm, unseating the inlet check valve and allowing air in from the EVAP air filter. When the diaphragm completes its upward movement, the LDP reed switch turns from closed to open.

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, allowing the PGM to monitor LDP pumping (diaphragm up/down) activity. During the pumping mode, the diaphragm will not move down far enough to open the vent valve.

The pumping cycle is repeated as the solenoid is turned on and off. When the evaporative system begins to pressurize, the pressure on the bottom of the diaphragm will begin to oppose the spring pressure, 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:
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.
The Charcoal Canister

EVAP/Purge Solenoid:
The duty cycle EVAP canister purge solenoid (DCP) regulates the rate of vapor flow from the EVAP canister to the intake manifold. The Powertrain Control Module (PCM) operates the solenoid.

During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid. When de-energized, no vapors are purged. The PCM de-energizes the solenoid during open loop operation.

The engine enters closed loop operation after it reaches a specified temperature and the time delay ends. During closed loop operation, the PCM cycles (energizes and de-energizes) the solenoid 5 or 10 times per second , depending upon operating conditions. The PCM varies the vapor flow rate by changing solenoid pulse width. Pulse width is the amount of time that the solenoid is energized. The PCM adjusts solenoid pulse width based on engine operating condition.

Vapor Canister:
A maintenance free, EVAP canister is used on all vehicles. The EVAP canister is filled with granules of an activated carbon mixture. Fuel vapors entering the EVAP canister are absorbed by the charcoal granules.

Fuel tank pressure vents into the EVAP canister. Fuel vapors are temporarily held in the canister until they can be drawn into the intake manifold. The duty cycle EVAP canister purge solenoid allows the EVAP canister to be purged at predetermined times and at certain engine operating conditions.

Hope this helps.

Dec 14, 2010 | 2001 Jeep Grand Cherokee

1 Answer

Leak detection pump sw or mechanical fault


can be caused by failure of the evaporation system leak detection pump or reed switch. When you turn your key on, the LDP sometimes comes on briefly to pressurize the fuel tank. The PCM enables a solenoid value in the pump to allow engine vacuum to shift a diaphram that pressurizes the system. Locate the LDP if the left rear bumper/fender well. With the engine running, remove the vacuum hose to see if vacuum from the engine is being supplied to the pump. If not, check the hose connection at the engine intake manifold. Repair or replace the hose as necessary to restore vacuum to the LDP.
If the engine vacuum is present, the problem may be with the pump or the electrical power to the pump solenoid. You can check the power to the solenoid by removing the connector and probing the connector with a 12 volt test light. Connect the test light clip to a ground point on the frame and probe the cable terminals. With the car running, one of the terminal should light the test light. If not, the problem is the wiring to the alternator. If the test light comes on, replace the LDP. Please let me know if you have any questions.


EVAP Leak Detection Pump 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 onboard 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.
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 0.25 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.
The LDP assembly consists of several parts. The solenoid is controlled by the PCM, and it connects the upper pump cavity to either engine vacuum or atmospheric pressure. A vent valve closes the EVAP system to atmosphere, sealing the system during leak Testing. The pump section of the LDP consists of a diaphragm that moves up and down to bring air in through the air filter and inlet check valve, and pump it out through an outlet check valve into the EVAP system. The diaphragm is pulled up by engine vacuum, and pushed down by spring pressure, as the LDP solenoid turns on and off.
The LDP also has a magnetic reed switch to signal diaphragm position to the PCM. When the diaphragm is down, the switch is closed, which sends a 12v (system voltage) signal to the PCM. When the diaphragm is up, the switch is open, and there is no voltage sent to the PCM. This allows the PCM to monitor LDP pumping action as it turns the LDP solenoid on and off.
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, allowing the PCM to monitor LDP pumping (diaphragm up/down) activity.
During the pumping mode, the diaphragm will not move down far enough to open the vent valve. The pumping cycle is repeated as the solenoid is turned on and off. When the evaporative system begins to pressurize, the pressure on the bottom of the diaphragm will begin to oppose the spring pressure, 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.
Diaphragm Upward Movement
When the PCM energizes the LDP solenoid, the solenoid blocks the atmospheric port leading through the EVAP air filter and at the same time opens the engine vacuum port to the pump cavity above the diaphragm. The diaphragm moves upward when vacuum above the diaphragm exceeds spring force. This upward movement closes the vent valve. It also causes low pressure below the diaphragm, unseating the inlet check valve and allowing air in from the EVAP air filter. When the diaphragm completes its upward movement, the LDP reed switch turns from closed to open.

Removal & Installation
The Leak Detection Pump (LDP) is located under the left quarter panel behind the left/rear wheel. It is attached to a two-piece support bracket. The LDP and LDP filter are replaced (serviced) as one unit.

  1. Remove stone shield behind left/rear wheel. Drill out plastic rivets for removal.
  2. Remove 3 LDP mounting bolts.
  3. Remove support bracket brace bolt.
  4. Loosen, but do not remove 2 support bracket nuts at frame rail.
  5. To separate and lower front section of two-piece support bracket, remove 3 attaching bolts on bottom of support bracket. While lowering support bracket, disconnect LDP wiring clip.
  6. Disconnect electrical connector at LDP.
  7. Carefully remove vapor/vacuum lines at LDP.
  8. Remove LDP.

To Install:
  1. Position LDP and carefully install vapor/vacuum lines to LDP and LDP filter.
    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.
  2. Connect electrical connector to LDP.
  3. While raising front section of support bracket, connect LDP wiring clip.
  4. Install 3 LDP mounting bolts.
  5. Join front and rear sections of two-piece support bracket by installing 3 bolts on bottom of support bracket. Do not tighten bolts at this time.
  6. Install support bracket brace bolt. Do not tighten bolt at this time.
  7. Tighten 2 support bracket nuts at frame rail and 3 support bracket bolts and brace bolt.
  8. Position stone shield behind left/rear wheel. Install new plastic rivets.
  9. jturcotte_55.gif

Nov 05, 2010 | 2000 Jeep Grand Cherokee

1 Answer

I have a 1998 v 6 dodge dakota sport with a p1495 trouble code how do i fix it


DTC P1495 - Leak Detection Pump Solenoid Circuit

WHEN MONITORED: Immediately after a cold start, with battery/ambient temperature between 4.4 °C (40 °F) . F and 32 °C (90 °F) . Coolant temperature within -12 °C (10 °F) of battery/ambient

SET CONDITION: The state of the solenoid circuit does not match the PCM's desired state.

POSSIBLE CAUSES:
* Wiring Harness Intermittent
* Leak Detection Pump
* Fused Ignition Switch Output
* LDP Solenoid Control Circuit Shorted To Ground
* LDP Solenoid Control Circuit Open
* PCM

Leak Detection Pump System
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.

SYMPTOM: P1490-LOW SPEED FAN CONTROL RELAY CIRCUIT
WHEN MONITORED: With the ignition ON. Battery voltage greater than 10 volts .

SET CONDITION: An open or shorted circuit is detected in the radiator fan relay control circuit.

POSSIBLE CAUSES:
* Low Speed Radiator Fan Relay Intermittent Operation
* Intermittent Condition
* Fused Ignition Switch Output Circuit
* Low Speed Radiator Fan Relay Resistance
* Low Speed Radiator Fan Relay Control Circuit Open
* Low Speed Radiator Fan Relay Control Circuit Short To Ground
* PCM


Notes
The Transmission/Transaxle Controller monitors the malfunction of sensors and actuators relating to Transmission/Transaxle Control. If any malfunction is detected, they inform the PCM by sending a signal - By illuminating the MIL and by setting the P0700 code.

P0700 means that a code has been set in the Transmission/Transaxle Controller. If P0700 is present, check for Transmission/Transaxle codes.

Hope helps (remember comment and rated this).

Aug 02, 2010 | Dodge Dakota Cars & Trucks

1 Answer

Code P1494


DTC P1494 - Leak Detection Pump Switch or Mechanical Fault

The causes are possibly an open or shorted switch sense circuit, a pump switch failure, or an open "fused ignition switch" output. First off, a model year 2001 is will still covered under the emissions warranty. That's federal law. So you should not have had to pay a penny for that repair since the Leak Detection Pump is an emission control device.

As is the Charcoal Canister. If that is bad there should be no charge for repair or replacement. I hope you saved the receipts because I think they owe you a bunch of money. If they give you an argument about it, call Chrysler and they will take care of it.

Now, are you ready to learn more about the Leak Detection Pump then you will ever need to know? Good! Here it is!

Leak Detection Pump (LDP) Operation And Diagnosis:

This article describes the theory of operation for the leak detection system. In addition, information is provided for each of the Diagnostic Trouble Codes (DTC's) as follows:

* 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 Monitor Pinched Hose Found
* P1494-Leak Detection Pump SW Or Mechanical Fault
* P1495-Leak Detection Pump Solenoid Circuit

Introduction:
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 (remember I said that?) 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.

Leak Detection Pump (LDP) Components:
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' H20(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.

The LDP assembly consists of several parts. The solenoid is controlled by the PCM, and it connects the upper pump cavity to either engine vacuum or atmospheric pressure. A vent valve closes the EVAP system to atmosphere, sealing the system during leak testing. The pump section of the LDP consists of a diaphragm that moves up and down to bring air in through the air filter and inlet check valve, and pump it out through an outlet check valve into the EVAP system.

The diaphragm is pulled up by engine vacuum, and pushed down by spring pressure, as the LDP solenoid turns on and off. The LDP also has a magnetic reed switch to signal diaphragm position to the PCM. When the diaphragm is down, the switch is closed, which sends a 12 V (system voltage) signal to the PCM. When the diaphragm is up, the switch is open, and there is no voltage sent to the PCM. This allows the PCM to monitor LDP pumping action as it turns the LDP solenoid on and off.

LDP At Rest (Not Powered):
When the LDP is at rest (no electrical/vacuum) the diaphragm is allowed to drop down if the internal (EVAP system) pressure is not greater than the return spring. The LDP solenoid blocks the engine vacuum port and opens the atmospheric pressure port connected through the EVAP system air filter. The vent valve is held open by the diaphragm. This allows the canister to see atmospheric pressure.

Diaphragm Upward Movement:
When the PCM energizes the LDP solenoid, the solenoid blocks the atmospheric port leading through the EVAP air filter and at the same time opens the engine vacuum port to the pump cavity above the diaphragm. The diaphragm moves upward when vacuum above the diaphragm exceeds spring force. This upward movement closes the vent valve. It also causes low pressure below the diaphragm, unseating the inlet check valve and allowing air in from the EVAP air filter. When the diaphragm completes its upward movement, the LDP reed switch turns from closed to open.

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, allowing the PGM to monitor LDP pumping (diaphragm up/down) activity. During the pumping mode, the diaphragm will not move down far enough to open the vent valve.

The pumping cycle is repeated as the solenoid is turned on and off. When the evaporative system begins to pressurize, the pressure on the bottom of the diaphragm will begin to oppose the spring pressure, 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:
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.

The Charcoal Canister

EVAP/Purge Solenoid:
The duty cycle EVAP canister purge solenoid (DCP) regulates the rate of vapor flow from the EVAP canister to the intake manifold. The Powertrain Control Module (PCM) operates the solenoid.

During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid. When de-energized, no vapors are purged. The PCM de-energizes the solenoid during open loop operation.

The engine enters closed loop operation after it reaches a specified temperature and the time delay ends. During closed loop operation, the PCM cycles (energizes and de-energizes) the solenoid 5 or 10 times per second , depending upon operating conditions. The PCM varies the vapor flow rate by changing solenoid pulse width. Pulse width is the amount of time that the solenoid is energized. The PCM adjusts solenoid pulse width based on engine operating condition.

Vapor Canister:
A maintenance free, EVAP canister is used on all vehicles. The EVAP canister is filled with granules of an activated carbon mixture. Fuel vapors entering the EVAP canister are absorbed by the charcoal granules.

Fuel tank pressure vents into the EVAP canister. Fuel vapors are temporarily held in the canister until they can be drawn into the intake manifold. The duty cycle EVAP canister purge solenoid allows the EVAP canister to be purged at predetermined times and at certain engine operating conditions.

Hope helps (remember rated and comment this).

Jun 17, 2010 | 2001 Jeep Grand Cherokee

1 Answer

2001 dodge neon check engine lite is on code 1495 showing


P1495 Leak Detection Pump Solenoid Circuit Open Or Shorted
Code P1495 is for the LDP solenoid circuit. (LDP-Leak Detection Pump). This is a system that seals off the evaporative system of the car and then pressurizes it with the LDP. The computer looks to see how long it takes to pressurize the system, (depending on fuel level) and then determines if the system is leaking. Emissions regulations require this to cut down on fuel vapours from escaping to the atmosphere.You will likely have to get a dealer to diagnose this, unless you can find a shop that has a manual and DRB scan tool.

Apr 09, 2009 | 2001 Dodge Neon

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