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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

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 August 28th, 2017, 07:32   #1
nikolay_ss
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Default VW MK4 ALH 2001 - Do I have CAN bus on the OBD2 port?

Hello,

I found some similar threads, but none of them was including the answer of my question.

When I connect to VCDS and click on test connections it says K1 and K2 are OK and CAN BUS says Not ready.

When I go to 19. CAN Gateway in VCDS it shows my CAN BUS and bla bla... everything seems okay. I also saw in 46. channel I think, can't remember correctly that Can bus is OK, but can I access it via OBD2 port or it's just for the instrument cluster if it's immo3, mine is immo2. I tried ELM327 and it works, but I want to connect there via arduino and can bus controller so I can make a small display and shows some info there.

Thanks for help!!
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Old August 28th, 2017, 08:00   #2
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Pins 6 and 14 of the OBD port are the CANBUS diagnostic lines, but MK4 did not have direct canbus diagnostics. VCDS needs to have a CANBUS car connected for the CANBUS test to work.

This doesn't mean that there aren't CANBUS connections from some modules to other modules. Common places to have a direct canbus is ecu to instrument cluster, ecu to automatic transmission module (if equipped), etc. But this is for internal module to module communication only.
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Old August 30th, 2017, 06:09   #3
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Thanks for your answer.

So how can I connect to CANBUS and read the messages which are processing from one module to another? From where I can get the signal? Should I try to find the wires behind the instrument cluster and try to read from there?

Thanks!
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Old August 30th, 2017, 06:18   #4
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What are you trying to do?

As Enabled's post says, that car has CAN, but DLC communications are done through the CAN Gateway, the CAN is just for module-to-module communication on that car. DLC communication is via the K-line setup.

There is also a paired wire communication dedicated for the CCM and the door modules (if equipped) and I think the radio might also be on this, not sure. The radios changed during these "internal CAN" years for our cars, mid-2002. The radio may also just use the K-line still.

I wondered about this once for diagnostic purposes. As I ended up finding out through process of elimination, I had a 2002 Jetta that had an SRS module that insisted the doors be unlocked. It thought the car was in a crash, or at least that portion of its post-crash logic was stuck on, so it kept telling the CCM to unlock the doors. And any lock signal given to the CCM (which it was getting, from all sources) was simply overridden. So somewhere in that CAN bus was a message packet being sent high priority (since SRS signals get this first) to the CCM.

But unless you have a mechanism to actually READ these packets, and decipher what they mean, I am not really sure what you could learn by monitoring the CAN bus directly. You can read voltages with a fast true RMS meter, but again, the packets are being transferred about so fast and so many that you'd need some way to know what it meant.
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Last edited by oilhammer; August 30th, 2017 at 06:23.
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Old August 30th, 2017, 09:33   #5
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Hey oilhammer, thanks for your comment, it was really helpful.
I am trying to read my engine channels and display them to a screen which I will put into my instrument cluster. But from your comment I understood thats not possibl for my engine. So I should find a way to read K line and work with it, right?
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Old August 30th, 2017, 10:12   #6
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If your trying to read the engine blocks (group 1 iIrc) you should not have a problem with VCDS.

If you replaced the radio with an aftermarket radio and it was not wired in correctly that could cause issues.
That's part of why I ran new power & speaker wires when I replaced mine.

Did you buy the real (not copy) VCDS cable?

Last edited by wonneber; August 30th, 2017 at 10:13. Reason: Clarity :)
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Old August 30th, 2017, 10:49   #7
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Sounds to me like he just wants a Scangauge or similar.

Not sure about what is available for the car though, as Europe did not get OBD2 like we did until later. Up through 2003 I think they used EOBD, and the DLC was down in the center console. My 2000 Golf even has the spot for it down there.
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Old August 31st, 2017, 02:48   #8
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Yes I can read the car's modules with VCDS, but I want to make a separate controller with a display and implement it into instrument cluster.
I found something that I think will work in my case. I need to test it.

https://github.com/ibanezgomez/FISBlocks
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Old August 31st, 2017, 06:24   #9
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Let us know what you find. Having a probe at the CAN in the Jetta and Touareg has been on my list of things to fiddle with for a while.

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Old August 31st, 2017, 06:28   #10
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They make contactless CAN readers (a little box that goes around the paired wires) but I would assume this just reads binary 1s and 0s, and unless you have a way to decipher the language it would have to be attached to something else?
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Old August 31st, 2017, 06:30   #11
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Yes, that's the idea. Hook it up to software to do packet analysis.
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