CAN-isolation relay help

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Adam87
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CAN-isolation relay help

Post by Adam87 » Sat Mar 04, 2017 10:55 pm

Hopefully someone who has fitted 'Lane Assist' can shed some light on the CAN-isolation relay,

Here is the wiring diagram for it
Image

And here is the relay next to the carrier
Image

The CAN-isolation relay is 3C0 951 253 A as in ETKA.

But the pins on the relay don't match the diagrams


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ciclo
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Re: CAN-isolation relay help

Post by ciclo » Sun Mar 05, 2017 12:05 pm

The problem is that the diagram is for T6 and the relay and relay adapter shown in the second image are for T5.

T6
3C0951253C

7E0937528

T5

3C0951253A

443937527

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Re: CAN-isolation relay help

Post by Adam87 » Sun Mar 05, 2017 12:20 pm

Ok, it makes sense, the T6 diagrams were used because of the ACC, do you have any detail of pin assignment for the T6 relay Fernando?


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Re: CAN-isolation relay help

Post by ciclo » Sun Mar 05, 2017 12:31 pm

The pin assignment depends on the relay adapter.

With a battery/multimeter you can also discover the relay operation. :)
edit:
adapter = holder
Last edited by ciclo on Sun Mar 05, 2017 7:07 pm, edited 2 times in total.

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Re: CAN-isolation relay help

Post by Adam87 » Sun Mar 05, 2017 2:32 pm

It looks correct for T5
Image
Image

T6 & T5 relays look to have the same pins
Image (T6)
T5 one pictured above,
And T6 one doesn't match the pins on the holder, unless the T6 holder has the pin numbers in a different order


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ciclo
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Re: CAN-isolation relay help

Post by ciclo » Sun Mar 05, 2017 7:02 pm

Adam87 wrote: And T6 one doesn't match the pins on the holder, unless the T6 holder has the pin numbers in a different order


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Exactly.
----
Everything else (your image with colored circles) is correct for proper operation.

I know people who have used two universal relays, one for Can High and one for Can Low (it seems to work correctly). :lol:

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Re: CAN-isolation relay help

Post by Adam87 » Sun Mar 05, 2017 8:03 pm

Great, thanks Fernando I wonder why it has to break the CAN lines to ACC / Lane assist? Is it incase of fault? Does it not bring up a fault code when relay breaks connection? Or is it satisfied because BCM knows it's supposed to be broken when it cuts the power?


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Re: CAN-isolation relay help

Post by ciclo » Mon Mar 06, 2017 8:23 am

Although I can think of several reasons, I honestly do not know it. Maybe someone can enlighten us about it.

Note that CAN lines work with +30, and the J428 and J769/J770 units work with +15.

If you have the T5 Lane change assist units you will also have to install the button, if you have T6 Lane change assist units it will work through an IC ready for it. I guess.

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Re: CAN-isolation relay help

Post by iichel » Mon Mar 06, 2017 9:03 am

ciclo wrote:
I know people who have used two universal relays, one for Can High and one for Can Low (it seems to work correctly). :lol:
I've done the Lane Change Assist retrofit on my Polo 6R.
The CAN Isolation Relay is indeed a tricky one. I decided against buying it since I found it simply too expensive.

What I've done is, taken two mini-relays.
One relay simply opens the Can Powertrain High with power off, the other one for Can Powertrain Low.
This works perfectly. Simply connect the T73a/8 to both 86 ports of the relays. Both 85 connections to +30 (fused, always).
Then you can connect the Can from i.e. PDC to the 30 port and the J770 to 87.
So far I've had no problems at all with this setup.

The main reason, I think, is to keep the CAN isolated from outside threat. Imagine, the Lane Assist or ACC open from the outside, it would be very easy to give a CAN command to open doors/deactivate alarm ;)
Powertrain CAN is, as far as I know, always accessible and doesn't switch off with +15.

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Re: CAN-isolation relay help

Post by ciclo » Mon Mar 06, 2017 9:44 am

You are great! Michel ... and you know it ... :lol:

You do not know how much I want that you get the Kessy in your 6R. :wink:

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Re: CAN-isolation relay help

Post by Adam87 » Mon Mar 06, 2017 10:00 am

Thanks iichel, that's great information, and makes sense!

The CAN relay has already been purchased so I will try to use it.

I hope 'Lane Assist' light is already installed in my instrument cluster and just needs activation, I don't see why it won't be installed.


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Re: CAN-isolation relay help

Post by iichel » Mon Mar 06, 2017 11:40 am

As ciclo rightfully suggested, the best way is simply to measure. Make a GND and a +12V, apply to some poles. You'll hear a click eventually.
Then simply measure with a multimeter the resistance between some poles.
Presto, you'll have the 'diagram' for the relay ;)

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