connecting to can gateway and maunufacturer warranty

[paulautosound]

what is the industry standard as regards connecting a device such as a Canbus alarm system to a vehicle. The alarm manufacturer advises to hardwire the device to CAN and the manufacturer {ford} have a advisory on their workshop manual warning against interfering with CAN wires as it could cause a module to become damaged or damage to the CAN gateway. The alarm is a read only passive device and does not transmit. given the secure nature of the gateway is this just a convenient get out for the manufacturer. It suggests that the manufacturer is able to blame any device that is added to the network for any possible module failures.

I realise this is probably very much a year one type of question but I would appreciate any opinions on this as its an ongoing issue for me as more and more manufacturers are trying to close off avenues for access to CAN using warranty as an excuse. Any help  appreciated 

[Hooovahh]

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@paulautosound wrote:

given the secure nature of the gateway is this just a convenient get out for the manufacturer. It suggests that the manufacturer is able to blame any device that is added to the network for any possible module failures. 

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Probably.  CAN is quite robust, and adding another device on the bus, especially in read only mode shouldn't effect anything meaningful.  However what if your device was wired incorrectly and your CANH and CANL wires were accidentally shorted together, or shorted to some high voltage source?  Well the CAN bus isn't that robust, and you'd lose communication.  Then what?  Well ECUs should protect for various inputs, but it is possible something will break.  OEMs can't predict what you'll do, or what will happen.  So their advice is almost always going to be to not mess with it.

If you are really concerned you can look into some kind of CAN isolation hardware.  I've seen these done a couple ways but the most popular method is some kind of optical isolation, where there the electrical connections of the bus are left as undisturbed as possible.  Some of these can get quite expensive, but I see PEAK CAN has some that are affordable, but I've never used them.

But honestly it likely doesn't matter.  Make sure it is wired properly, and make sure the connections are robust, solid, and won't break over time and you'll probably be fine.  And in a read-only mode there isn't any worry that your device will put too much traffic on the bus, or accidentally send requests that reset ECUs for example.