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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old December 13th, 2017, 10:54   #1
Join Date: Dec 2016
Location: Nc
Unhappy Fried something in CAN bus. Kicking myself...

So after successfully completing a 5 speed swap on my 04 bew golf I started on the wiring. Being in too much of a rush I "accidentally" sent 12v down the orange and black CAN high wire at the tcu harness. No more start....
No glow plug light, no cell, just turns over and over. I have it at a shop right now they have tried a second ecu and cluster. They are able to communicate with all modules but say they are not communicating with each other. The 109 relay seems to be fine, so I'm pretty sure I fried at least one module in the CAN network. I'm going to the shop tomorrow and will try to post a full scan. They want to put the load reduction relay 175 back to stock instead of the 53 I have in there now for safety switch and the other wires I cut for reverse and speed. Sorry so long, was hoping someone would have some insight other than the obvious huge mistake I made... Would like to have a working car after putting all the time and money so far.
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Old February 7th, 2018, 07:57   #2
Join Date: Dec 2016
Location: Nc

any ideas?
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Old February 7th, 2018, 08:23   #3
Vince Waldon
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Join Date: Apr 2009
Location: Edmonton Alberta Canada

Originally Posted by Trevor801 View Post
I'm going to the shop tomorrow and will try to post a full scan.
This was a good idea.
Vince Waldon Edmonton AB Canada

Note: The above is to the best of my knowledge- but at the end of the day simply interweb opinion, worth EXACTLY what you paid for it, and if used done so at your own risk.
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Old February 7th, 2018, 19:07   #4
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Join Date: Sep 2016
Location: WA
TDI(s): 2004 Wagon

I just spent some time looking at the CAN on my 2004 BEW Wagon.

Do you have Vag Com? If so, you should know pretty quick if there is activity on the system.
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Old February 8th, 2018, 19:12   #5
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Join Date: Oct 2011
Location: Monroe, NY, USA

Long shot.
Did anyone check the fuses?
Do all the dash lights com on with the key?
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Old February 10th, 2018, 09:22   #6
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Join Date: Sep 2004
Location: Marengo, IL

There is another piece to the puzzle you need to consider. I had a lot of problems with my swap from a gas to tdi and found the comfort module was not compatible with the older swap stuff. Lack of communication can mean something is taking the communication down like a short to ground. You could have fried something like your comfort module and it takes the signal down to the ground. Try unplugging your comfort module and see if the ecu comes to life. I would get a wire diagram and trace every path of the can bus out and see what it feeds. Usually in a case of sending voltage down a wrong path like you did will fry something out. It could be a wire or module but most likely a module if you don't smell any burning. With the ecu and the cluster swapped I would look at anything else in the path. I sparked 12 volts to a Passat gasser can bus and fried the throttle position sensor out. If you don't have a good wire diagram just try unhooking everything you can but still leaving the ecu and cluster and the test port connected. verify communication and see if that will fire everything off. In these can bus cars there are end points for the can bus in the window motor computers.

Last edited by tgray; February 10th, 2018 at 09:26. Reason: wrong advice
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Old February 10th, 2018, 14:49   #7
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Join Date: Sep 2014
Location: Arthur Ont.

Very first thing to do is check pin 6 to 14 in your dlc connector with an ohm meter. You should have roughly 60ohms. The bus system has two 120ohm resistors wired in parallel, one on either end to eliminate unwanted voltages. Blowing one or both will drastically effect the bus operation. Best of luck,
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Old April 3rd, 2018, 10:30   #8
Join Date: Dec 2016
Location: Nc

thanks for the leads guys. Hoping to have a scan to post soon. Turns out they are not reading the 60 ohms between the two pins at the test port. If it is sounding like a fried resistor, where are they possibly located. Are they located in a module, cluster or possibly hidden somewhere in the harness. We can talk to and see the modules but are not getting a cel or glowplug light with key on. Trying to get the ecu powertrain back up and running.
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