Unlock/Lock – How Distributed Systems Help You

Posted On December 6, 2009 at 6:36 pm by / No Comments / CAN BUS

So you want to Unlock and Lock the doors using the CAN BUS?  Well I’ve got good news for you, you can. Well sort of…

Because most modern vehicles have distributive electronic systems, unlock/lock type functionality is often done via a CAN BUS message by the OEM themselves.  Typically if the RFA module (controller that receives commands from the key fob) is separate from the controller(s) that actuate the door locks themselves, then this command will occur over the CAN BUS.

So how do you know if this RFA is separate? You will most likely have to consult a wiring manual such as the Mitchell Guide.

So if the modules are separate, you will have to connect to the vehicle’s body CAN BUS (this is often separate from the Powertrain bus or OBDII CAN BUS).  Once you’ve found this network, you will have to monitor the network for the Unlock or Lock commands by using the factory key fob and watching for a new message that shows up or data that changes at the same instant that you press the key fob lock/unlock buttons.  Do this about 3 to 4 times and you’ll find the message that controls the Unlock and Lock commands.  If you don’t find it, try a little bit more, but remember it might not be there.

So once you have the message, you can test it.  To do this, simply send a message with the same Arbitration ID and Data as the one that you discovered.  Then see if the doors lock/unlock.  If they do, you’ve found it.  If not, try again, perhaps you found a message related to a door unlock/lock procedure such as disarm or dome light status.

Again, if you need help, let me know..

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