Mechanics

I NEED TO FIX A PROBLEM WITH THE EMISSION SYSTEM

1999 Dodge Dakota • 150,000 miles

My truck keeps displaying code P1495. I took the battery tray out and looked for the LDP, but there is nothing there, and looks like nothing had ever been there. I bought this truck used in OK, where they do no emissions testing, but I live in Texas and need to get it inspected. Why would I keep getting this code if my truck was not equipped with a Leak Detection System? Is it possible somebody in the past installed an incorrect PCM?
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Kmbrock100
March 14, 2012.




I asked a couple of fellow moderators to weigh in on your issue about possibly someone replaced the pcm with a used one that had the LDP solenoid and possibly your truck didnt cone with it.
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Saturntech9
Mar 15, 2012.
Or maybe the circuit was also used for something else that is now broken. When I erase the code with my scanner it re-codes in about 5 seconds or less. There are no other codes appearing in the system, only p1495 and sometimes p1494 too.


Tiny
Kmbrock100
Mar 15, 2012.
This is a different expert. It really has to have an LDP if it's obd2 which this truck is. It may have been removed by a previous owner but it's supposed to have one.

http://i1198.photobucket.com/albums/aa448/Wrenchtech/78380751.gif



Wrenchtech
Mar 15, 2012.
Thanks for weighing in on this one wrenchtech. Nice diagram.


Saturntech9
Mar 15, 2012.
I posted the wire colors of the wires your looking for. Your going to have to scour the wire harness to find those wires.


Saturntech9
Mar 15, 2012.
I think I found a place under the power block where the pump could have been attached. Unfortunately, whoever removed it did a very thorough job and there are no disconnected or capped hoses. I found a connector under the power block that probably went to it. It had a factory-looking cap over the end of it, which is why I did not notice it. When I buy a LDP, should I just cut into one of the hoses and install a tee? The check engine light has probably been on forever, and I dont understand why someone would want to completely eliminate the LDP system since it could not hurt anything.


Tiny
Kmbrock100
Mar 15, 2012.
http://i1198.photobucket.com/albums/aa448/Wrenchtech/91114825.gif

http://i1198.photobucket.com/albums/aa448/Wrenchtech/78380773.gif

Leak Detection Pump (LDP) Operation And Diagnosis

This bulletin 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 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.



Wrenchtech
Mar 15, 2012.
So it mounts right the battery box thats a nice diagram thanks wrenchtech for all the help. Looks like you have all the info you need to reinstall missing componets.


Saturntech9
Mar 15, 2012.
It's a 4 pin, flat plug that you're looking for.

http://i1198.photobucket.com/albums/aa448/Wrenchtech/78381628.gif


Wrenchtech
Mar 15, 2012.

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