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P1494-Leak Detection Pump Pressure Switch Or Mechanical Fault

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Posted on Jan 02, 2017

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SOURCE: p1494 code

It means you aren't tightening the gas cap down tight, or the vent in the gas cap isn't sealing. Open the gas cap, and look at the center. Take a punch and jiggle the center, which is a valve. This will usually re-seat the valve... or replace the cap. Every so often the computer will pump air into the fuel tank to determine if there's a poor seal in the air space above fuel. If it doesn't find pressure holding, then the error code is logged.

Posted on Aug 08, 2008

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SOURCE: leak detection pump sw or

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

Posted on Nov 05, 2010

Testimonial: "thank you this was very helpful"

  • 76630 Answers

SOURCE: Trouble code P1494

These are all related sensors and active devices of the evap system, clear the code and replace the fuel cap.

Posted on Nov 12, 2008

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what is a leak detection pump switch or evap

Posted on Jun 15, 2009

  • 1757 Answers

SOURCE: need to know where the leak detection pump

NOTE: The EVAP System normally does not fail during the lifetime of the Van. Any failures could normally be blamed on the cannister (which is expensive) and the hose having leaks/bad connections.
The leak detection pump is located under the vehicle on top of the engine cradle (big black brace under the engine) just below and towards the front of the driver side near the steering gear (not the pump) It is a cylindercal shape (like a soda can(okay beer) can) with larger (1/2 to 5/8 in) sized hoses attached. One hose on one side the on the cannister and other hose on the other side.

Posted on Nov 21, 2009

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2 Answers

Que significa codigo p1494

P1494 Leak detection pump pressure switch or mechanical fault

Jul 01, 2014 | 1999 Jeep Grand Cherokee

1 Answer


P1494: Leak detection pump pressure switch or mechanical fault
not sure what system that pertains to but this is the definition i get from my reader software.

Nov 03, 2012 | 2001 Chrysler Concorde

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Engine light stays on code p1494

P1494 code is a leak detection pump switch or mechanical fault, leak detection pump switch does not respond to input. The leak detection pump (if equipped) is located under the air filter housing on models through 2001. Check if the vapor and vacuum lines are securely connected to the leak detection pump or a diagonstic trouble code my be set like this. The leak detection pump switch may be bad and need replaced.

Sep 27, 2011 | 2000 Jeep Cherokee

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P1494 Leak detection pump pressure switch or mechanical fault
no idea what it means though but i would assume its something to do with the tank vapour extraction pump more they put on the more their is to go wrong

Sep 15, 2011 | Jeep Grand Cherokee Cars & Trucks

1 Answer

My 2001 Dodge Intrepid has the P1494 code on it and the motor light comes on. Do I have to fix it right away or what will happen if I don't?

Leak Detection Pressure pump pressure switch or mechanical fault(bad pump). basically tells you that the system detected a leak. It's not a have to fix it quick problem, but it is annoying. First make sure that when you gas up the car, when you go and put on the fuel cap, that it is on there tight and make it click a couple of times. Check the seal on the gas cap and make sure it's not dried up and cracked, if so replace. The other thing could be a bad pressure switch or a bad leak detection pressure pump.

Sep 03, 2011 | 2002 Jeep Liberty

1 Answer

Trouble code p1494 p1495

P1494 Leak detection pump pressure switch or mechanical fault
P1495 Leak detection pump solenoid circuit
you have a problem with the fume extraction circuit like a motor or something

Apr 24, 2011 | 2002 Chrysler PT Cruiser

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.

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

My service engine soon light is on and I have been told the code is 1494. What does that mean?

P1494 is a Leak Detection Pump Switch or Mechanical Fault. 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). This is a problem with evaporative emissions system and should not affect drivability. If this was helpful please leave positive rating.

Nov 30, 2010 | 1999 Dodge Avenger

2 Answers


The Dodge P1494 engine light code means Leak Detection Pump Switch or Mechanical Fault. A proper diagnosis must be done, you can't simply replace the LDP and expect that to fix the problem. It shouldn't hurt anything to keep driving it for a while until you can get it fixed.
There is a technical service bulletin that applies to your vehicle and it mentions that code specifically. I'm including it here for your information: TSB-18-01-00
SUBJECT: Misdiagnosed Leak Detection Pump Systems With DTC P1494, P0442, P0455, OR P0456.
MODELS: 1997 - 2000 (LH) Concorde/Intrepid/LHS/300M/Vision and others
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.


Hope helps (remember rated and comment this).

Sep 08, 2010 | Dodge Dakota Cars & Trucks

1 Answer

96 dodge caravan code p1494

P1494 Leak detection pump pressure or mechanical fault, hope this helps

May 15, 2009 | 1996 Dodge Caravan

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