# Leak Detection Pump, has anyone successfully by-passed it?



## Veedubgti (Mar 5, 2001)

After recoding my ECM from an Automatic to a 5-Speed, I am proud to say that I am down to only 1 DTC: 17881 - EVAP Leak Detection Pump: Open Circuit. I did not incoporate the LDP into my AEB 1.8t swap. Has anyone with either an OBD2 ABA or a 1.8t swap successfully eliminated this DTC? If so, could you please share your experience? I do know that the resistance between contacts on the pump motor for AEB engine code are as follows......
resistance between contacts 1 and 3 = 640-720ohms
resistance between contacts 2 and 3 = 17.5-27.5ohms
It can't be as easy as putting in appropriate resistors in there is it?








If anyone out there has accomplished this please speak up or at least lets figure it out together







Thanks
pic for views:










_Modified by Veedubgti at 5:23 PM 6-3-2004_


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## VR6GTI'00' (Oct 31, 2001)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (Veedubgti)*

You are getting a code for failing the check to see if the pump is in the system. That can easily be bypassed using the appropriate resistor. If that passes then the ECU looks for the pressure switch to close within a set length of time (checks to see that the pump is pressurizing the system). After the system has pressurized the pump shuts off and the ECU times the period until the pump turns on again (measures the leak rate). Both of those times have to be right. That bit is more difficult to kluge. I found that it was easier to make the system work properly than to fool it.
While I am talking about kluges (this one doesn't apply to AEB) ... . I used resistors to simulate the Secondary Air System because there is no room on the block for the SA pump in the mkII. The ECU looks for the coil of the SA Relay and the SA Vacuum Valve. In the swap post (see my sig) I detailed how to use resistors to pass those tests. But, there is another test that I was not aware of. The ECU looks for the wide band O2 sensor to go more lean when the SA pump comes on with cold start. When the engine starts cold the fuel mixture defaults to rich, -100%. As soon as the wide band O2 sensor comes on line (but before the ECU goes closed loop) the SA pump scomes on and the ECU looks for the wide band O2 to go to the range -45% to 100%. If it doesn't then the Readiness check fails and there is a code for Incorrect Secondary Air Flow. I am considering either reinstalling the SA relay and use it to switch a fixed value to the ECU O2 input during SA pump operation or possibly remote locating the pump and using the system as it was designed.


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## vr6swap (Aug 17, 2001)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (Veedubgti)*

APR has a program for the AEB motor that turns off the EVAP system (and the rear o2 sensor). You say in your sig that your car is already APR'ed, so you might want to look into this one. 
Futrell Autowerks has the exclusive on it, don't bother calling APR 'cause they don't want to know.


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## punkassjim (Sep 22, 2002)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (vr6swap)*

yeah, I called APR and they denied knowledge of such a feature.
Anyway, hey Veedubgti, did you delete the plug for the LDP from your wiring harness? Because if you didn't, you could just plug the pump in and that code will go away. Right now I just have my LDP sitting in my spare tire well, plugged into nothing but the electrical connector. Every couple days I get a CEL for incorrect flow.
Check out VR6GTI'00's swap thread, page 15 i believe, for the diagram of how to hook up the hoses to the LDP and make it work correctly. http://****************.com/smile/emthup.gif


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## Veedubgti (Mar 5, 2001)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (vr6swap)*


_Quote, originally posted by *vr6swap* »_APR has a program for the AEB motor that turns off the EVAP system (and the rear o2 sensor). You say in your sig that your car is already APR'ed, so you might want to look into this one. 
Futrell Autowerks has the exclusive on it, don't bother calling APR 'cause they don't want to know.

Already looked into it, I spoke to Dean F about this. He told me that the code I have will remain even with the APR "emissionless software" I do not get any of the codes that this software deletes(I have rear O2 and EVAP), so it isn't a worthwhile update for me. Although Dean F. did say that APR was working on a new version of that software to fix the code I do get. I'll just have to wait and see.


_Modified by Veedubgti at 11:12 AM 6-4-2004_


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## Veedubgti (Mar 5, 2001)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (punkassjim)*


_Quote, originally posted by *punkassjim* »_Anyway, hey Veedubgti, did you delete the plug for the LDP from your wiring harness? Because if you didn't, you could just plug the pump in and that code will go away. Right now I just have my LDP sitting in my spare tire well, plugged into nothing but the electrical connector. Every couple days I get a CEL for incorrect flow.
Check out VR6GTI'00's swap thread, page 15 i believe, for the diagram of how to hook up the hoses to the LDP and make it work correctly. http://****************.com/smile/emthup.gif 

I honestly can't remember if I kept the wiring or not, it was almost three years since I wired the swap. I was thinking of grabbing a Mk3 LDP and trying that. When I was running 3-4 codes constantly, I didn't really care about the LDP code. Now that it's my ONLY one I GOTTA GET RID OF IT!!!!!


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## JNXtheband (Jul 27, 2000)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (Veedubgti)*

if you really wanted to im sure you could use the signal from the airpump to trigger a relay that would send a higher voltage to the o2 sensor connector which would fool the ecu twice. all you would need to do is isolate this new circuit with diodes so it dosent interfere with the regular processes of the sensors.
Its an idea i was thinking of but dismissed it because its too much work just to get rid of a CEL.


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## VR6GTI'00' (Oct 31, 2001)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (JNXtheband)*


_Quote, originally posted by *JNXtheband* »_if you really wanted to im sure you could use the signal from the airpump to trigger a relay that would send a higher voltage to the o2 sensor connector which would fool the ecu twice. all you would need to do is isolate this new circuit with diodes so it dosent interfere with the regular processes of the sensors.
Its an idea i was thinking of but dismissed it because its too much work just to get rid of a CEL.

This is for secondary air with wideband O2. Not for LDP.
Sorry for mixing topics in one thread.


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## Veedubgti (Mar 5, 2001)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (VR6GTI'00')*

Stay on topic!


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## all-starr-me (Jul 14, 2003)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (Veedubgti)*

I know its not on topic exactly, but it you wire in an o2 simulator from casper electronics as the second o2 sensor then your secondary air injection won't get anymore cel's and you can run a high flow cat that would nomally set off that sensor


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## VR6GTI'00' (Oct 31, 2001)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (all-starr-me)*


_Quote, originally posted by *all-starr-me* »_I know its not on topic exactly, but it you wire in an o2 simulator from casper electronics as the second o2 sensor then your secondary air injection won't get anymore cel's and you can run a high flow cat that would nomally set off that sensor

Perpetuating the off topic discussion of Secondary Air.








Casper's website is under reconstruction. From this site ( http://www.mkiv.com/techarticl...ator/ ) it appears that the simulator is narrowband?
Does a high flow cat throw incorrect secondary air flow codes? I thought that the wideband O2 sensor was in front of the cat?


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## vr6swap (Aug 17, 2001)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (VR6GTI'00')*

*OFF TOPIC FREE-FOR-ALL!!* Woot.
There's a thread going in the 1.8T forum about various methods to defeat or otherwise fool the rear O2 sensor, using spark plug thread chasers to move the sensor out of the EG stream a little, or by using DIY or commercially available simulators to convince the ECU the sensor's still there and working. A worthwhile read, which is rare in the MK4 forum Jr.
Now, back on topic....if you have the LDP plugged up to the harness, but not hooked up to the EVAP system, would you want to loop the inlet/outlet with some hose, so that the pump would at least think it's doing something? 
I checked out Louis's diagram showing how to integrate the LDP into an A2 evap system, anybody know if a Passat LDP is the same? 




_Modified by vr6swap at 6:13 PM 6-6-2004_


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## VR6GTI'00' (Oct 31, 2001)

*Re: Leak Detection Pump, has anyone successfully by-passed it? (vr6swap)*


_Quote, originally posted by *vr6swap* »_*OFF TOPIC FREE-FOR-ALL!!* Woot.
There's a thread going in the 1.8T forum about various methods to defeat or otherwise fool the rear O2 sensor, using spark plug thread chasers to move the sensor out of the EG stream a little, or by using DIY or commercially available simulators to convince the ECU the sensor's still there and working. A worthwhile read, which is rare in the MK4 forum Jr.
Now, back on topic....if you have the LDP plugged up to the harness, but not hooked up to the EVAP system, would you want to loop the inlet/outlet with some hose, so that the pump would at least think it's doing something? 
I checked out Louis's diagram showing how to integrate the LDP into an A2 evap system, anybody know if a Passat LDP is the same?

The loop of tube works. The pump thinks it's pumping and nothing leaks. The N80 valve has to be hooked up electrically too. I had it hooked up to the vacuum hose on the LDP for awhile so that it wasn't just a vacuum leak when it cycled.


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