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Thread: LDP traced to bad ECU?

  1. #1
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    LDP traced to bad ECU?

    Hi wrenchers-
    I am a slow learner, and sometimes replace every inexpensive part before doing a full investigation due to time / money balance. My daughter drove home to CT from school in NC and brought home her C6A6 3.2q with CEL illuminated. I plugged in and found P2404, did some research, put it up on the hoist and looked for vacuum leaks, etc. replaced purge valve. swapped the two relays J757 and identical next to it Fuel pump? reset code. Old purge valve would not hold vacuum so I was somewhat hopeful. replaced gas cap then ran 070 and it tests good. run 071 and it aborts, reed never opens. Pull the fenderwell and listen during an 071 and ldp is silent. Pull the plug and it has 13V on pin1, 28" vacuum on source. the pin 3? solonoid ohm'd out OK- 16 (I forget) but had "weird" voltage at pin 2, like 8-12 to ground. It pained my but ordered and LDP, installed it and got nothing. I then built a test rig, with a battery, a vacuum pump, a balloon or 20 and played with old LDP. It pump fine, and although the contact never went under about 800 ohms it did change value consistently when pumped up.
    I think I found the 17pin connector by ECU, everything looked perfect, and so did ECU. I did not check the wire for integrity from LDP plug to the connector pin. Napa wanted $50 for a back pin test kit and I wasn't in the mood.

    I believe it was really running 071, but the pump never attempted to run, so it was not getting a ground through ECU. Could be wire, but no signs of a rub or melt. If I had the car another day I would have done more.

    I did the brakes, and front wheel bearings, and she drove it from CT back to NC.

    So now the car is in NC for a year, it will throw a code after a few cycles. Do I get a junk ECU and try to code it myself with vag-com? I will need to go to NC ( I do work there a few times a year) and hack the tamper screws out and everything else in a parking lot with exactly the tools I carry with me.
    Dealer is out- I'd buy her a Bluetooth OBDII reset tool for a year.
    Can anybody with VIN and full VAG-COM status flash a used PROM / ECU without the old ECU for under $700?
    Thanks for your input!

  2. #2
    Benevolent Dictator Uwe's Avatar
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    I don't think you can install a replacement ECU in that car with VCDS; I believe that's going to be a GeKo challenge/response thing.

    I'm reasonably confident that someone like Jack could do an identity transfer if he had both ECUs, but that doesn't seem practical.

    Honestly, I think verifying wire integrity between the ECU and the LDP pump should be done first anyway.

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

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  4. #3
    NostraJackAss Jack@European_Parts's Avatar
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    I don't think you can install a replacement ECU in that car with VCDS; I believe that's going to be a GeKo challenge/response thing.

    I'm reasonably confident that someone like Jack could do an identity transfer if he had both ECUs, but that doesn't seem practical.

    Honestly, I think verifying wire integrity between the ECU and the LDP pump should be done first anyway.

    -Uwe-

    Agreed Uwe ............

    Check the wiring and FYI the bad vacuum or failure of sufficient vacuum is what causes an ECU driver to be over worked and melt down as a result of trying to run the pump for extended amounts of time.

    The same is a result if the tank is always ran low on fuel or the gas cap was leaking again causing an over use of the test to perform the operation.
    An additional brake vacuum pump + reservoir are helpful to isolate the system from intake vacuum too.

    A load reduction relay wired in between the LDP and ECU works very well to relieve and protect the ecu from this happening or after a replacement.

    Many fail to listen to this advice sadly...........

    Let me know if I can help........
    Last edited by Jack@European_Parts; 07-31-2017 at 03:02 PM.
    European Parts Emporium/Performance / Immobilizer Solutions EPE
    Certified Master Trained NY/BAR/BAD 7076062/ASE/SAE/NASTF Legal Factory Authorized/Licensed GeKo/FaZit # 403738
    Specializing in Custom Services IE: "welding-fabrication" / EPA-SMOG Update or Pass-Thru-Programming / Data Transfer / Immobilizers & OEM Quality Parts
    Above Magic! No Written record, AUTO-SCAN or Appointment = NO HELP!
    www.FixMyEuro.com <<<<<CLICK HERE! or vwemporium@aol.com ( JPPSG & Unverified members need not PM me & Please don't email or call facility for free tech support...use the forum )
    Getting you CONTROL again of your property - TAKE IT! In Conjunction with.........

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    I understand, and think it was probably the purge valve failure that lead to the high cycle on LDP. I have read many of your posts on the subject prior to posting myself. I tried to follow your diagnosis path, but ran out of time with the car to test wire. Would have been easier with a helper, but didn't get it done. I have a subscription to Bentley, but it is on my XP laptop, and is a hassle electronically. Is Erwin any better?

    SIA will replace that channel of the ECU but takes 5 days. I might need to fly down rent me a car, then drive to her school and rent her a car, cut security screws, and ship ecu , go to my job for 4 days, then install- test . Testing wires in a NC parking lot in mid summer- ughh. When I tested the pin at LDP plug it had voltage- and a broken wire would probably not, a toasted transistor could.

    Thanks for your help Jack, will let you know how it plays out. It might wait until she drives back to CT. If so I would set it up at your shop in NY.

    -Peter

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  8. #5
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    Thanks Uwe- I read a few posts here indicating it was possible to change identity via VCDS. I also expected it would take a lot of time with CD player, nav etc. to get them all to talk to a foreign ECU. One procedure required getting Audi to tell me codes from VIN, not optimistic they would do that for me.

  9. #6
    NostraJackAss Jack@European_Parts's Avatar
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    10-4 thanks Pete.......let me know if I can help.
    European Parts Emporium/Performance / Immobilizer Solutions EPE
    Certified Master Trained NY/BAR/BAD 7076062/ASE/SAE/NASTF Legal Factory Authorized/Licensed GeKo/FaZit # 403738
    Specializing in Custom Services IE: "welding-fabrication" / EPA-SMOG Update or Pass-Thru-Programming / Data Transfer / Immobilizers & OEM Quality Parts
    Above Magic! No Written record, AUTO-SCAN or Appointment = NO HELP!
    www.FixMyEuro.com <<<<<CLICK HERE! or vwemporium@aol.com ( JPPSG & Unverified members need not PM me & Please don't email or call facility for free tech support...use the forum )
    Getting you CONTROL again of your property - TAKE IT! In Conjunction with.........

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