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VW B5 Passat TDIs This is a general discussion about B5 Passat(>98 (2004-2005 in North America)). Non TDI related postings will be moved or removed.

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Old February 19th, 2019, 10:17   #1
DrWorm
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Default ECM testing & repair...

We have a 2005 Passat TDI Wagon. The ECM is sporadically not sending the ground signal to the N75 valve and it is throwing an underboost and emissions workshop message. It clears itself and can be fine for two days or two weeks before it comes back.
Can anyone recommend where to send the ECM out for testing and possible repair?
Thanks
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Old February 19th, 2019, 13:11   #2
d0u8l3m
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It's more likely a cut in the wiring loom somewhere, rather than the ECU having any issues. The wire loom for the N75 gets hard and brittle and can slice a wire if its cracked or cut. Last year I had an issue with my car going into limp mode, and upon further inspection, the wiring from the n75 had a cut in one of the wires caused by the sleeving. Spliced it back together and all issues resolved.

If you end up thinking its the ECU its not hard to backup yours. Buy a used one on ebay or go go the junk yard and find one, and buy a BDM tool. Then you can just do a full flash read and write it to the new ecu.
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Old February 19th, 2019, 19:56   #3
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is there a 05 tdi specific BDM tool or are they generic? what's a good one
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Old February 20th, 2019, 04:51   #4
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I should have noted the ECM is definitely the issue. We checked pin 29 to the ECM and when the "emission workshop" comes on there is no ground to the N75 and the ground is fine when the fault is not triggered. At first we thought it was the harness and ran a new circuit for the ground but the issue persisted.
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Old February 20th, 2019, 07:15   #5
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The ECU will disable the output to the N75 when a fault occurs. What you are describing is normal behavior of the ECU.

When operating properly, the ground to the N75 is a pulse-width modulated signal with a 20-80% duty cycle.

What code is set when the problem occurs?
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Old February 20th, 2019, 08:07   #6
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The generic code is P0243 Turbocharger/Supercharger Wastegate Solenoid "A" and it throws the "Emissions Workshop". If it's acting up the code will show as pending after it's cleared and it comes up instantly when you turn the key.
When this first happened in December I found a hole worn in a vacuum hose and replaced it along with the N75 valve but it made no difference and it still comes and goes at random.
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Old February 20th, 2019, 08:13   #7
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Quote:
Originally Posted by afarfalla View Post
is there a 05 tdi specific BDM tool or are they generic? what's a good one

BDM stands for Background Debugging Mode. Any tool that supports this protocol will work. Original tools are best, but for personal use, I'd recommend the latest Ktag knockoffs that are on ebay.

OP, definitely double check continuity in your harness, as well as probe the PWM signal with a scope if available.
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Old February 20th, 2019, 14:12   #8
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Quote:
Originally Posted by DrWorm View Post
The generic code is P0243 Turbocharger/Supercharger Wastegate Solenoid "A" and it throws the "Emissions Workshop".
I'm assuming you have replaced the N75 valve?
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Old February 20th, 2019, 17:53   #9
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Quote:
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I'm assuming you have replaced the N75 valve?
Yes, it has a new N75 valve and there are no vacuum leaks, no leaks in the charge hoses and the turbo actuator moves when vacuum is put to it.
When we initially discovered the the N75 was not getting the ground from the ECM we figured it was an issue with the wiring harness so a new circuit was created by pinning a new ground wire from the ECM to the N75 valve to bypass the harness. It was fine for two days and it started acting up again. We verified the continuity of the new circuit so I'm sure it's not the wiring harness.
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Old February 20th, 2019, 19:23   #10
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The code is a circuit code, so it is definitely electrical. The positive side of the circuit could also be at fault. The N75 is fed from a 15 amp fuse in the ECU box at the base of the windshield. It might be worth checking that the N75 is receiving 12v as well. Maybe run a quick and dirty overlay for a couple days to be sure. I have never seen a failure in an EDC16 ECU output driver, but I have seen a few EDC15 ECU's with cracked solder joints at 400k +.

Too bad you weren't closer. I have BHW ecu's stacked like cordwood here...
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Old February 21st, 2019, 06:11   #11
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http://forums.tdiclub.com/showthread...d.php?t=178482

I am interested in who repairs these also, I had same issue with my 2001 ALH. I replaced the ecu and no further problems. Seems there is a diode on that circuit that is in the ecu that may have failed. We did not see any signs of water migration or cracks, some signs of heat though.
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Old February 21st, 2019, 06:15   #12
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http://forums.tdiclub.com/showthread.php?t=178482

Forgot about this one
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Old February 21st, 2019, 12:07   #13
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Quote:
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Thank you very much for the links. I didn't think to search the other forums and just stuck with the B5 posts.
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Old February 21st, 2019, 12:17   #14
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You bet, I am never on this forum either, just happened to be nosing around trying to learn a bit about the Passat BV43
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