Any Can bus experts?
Thread Starter
Teching In
Joined: Nov 2012
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Any Can bus experts? I am currently working on a project involving some hacking on the my GM can bus.
I am wondering if there are any folks out there who are real familiar with automotive Can Buses. Familiarity with GMs implementation would be even better.
One example question of the many I have is:
Does the BCM need to have a matching VIN in order to talk to the ECM?
If yes, how does that security work, will the BCM not send out messages unless that is verified? Or will the ECM not listen to any BCM messages unless they match? Or ....?
If anybody wants to impart some knowledge I would love the help.
Thanks,
Pat
I am wondering if there are any folks out there who are real familiar with automotive Can Buses. Familiarity with GMs implementation would be even better.
One example question of the many I have is:
Does the BCM need to have a matching VIN in order to talk to the ECM?
If yes, how does that security work, will the BCM not send out messages unless that is verified? Or will the ECM not listen to any BCM messages unless they match? Or ....?
If anybody wants to impart some knowledge I would love the help.
Thanks,
Pat
I'm not an expert but I have some info on these. The communicaion on 4th gens primitive by modern standards.
The BCM does not store a VIN, neither does the instrument cluster. For security, the BCM is looking for the proper resistance from the key, which will only be one of 15 possibilities. The BCM is programmed by whichever key resistance it reads the very first time it is powered up when new. For the rest of it's life, the BCM will look for that resistence value for security.
When the resistance matches, the BCM will power an anti theft relay to allow the starter to function, and the BCM will also send a fuel enable signal to the PCM so the engine will run.
The BCM does not store a VIN, neither does the instrument cluster. For security, the BCM is looking for the proper resistance from the key, which will only be one of 15 possibilities. The BCM is programmed by whichever key resistance it reads the very first time it is powered up when new. For the rest of it's life, the BCM will look for that resistence value for security.
When the resistance matches, the BCM will power an anti theft relay to allow the starter to function, and the BCM will also send a fuel enable signal to the PCM so the engine will run.
Staging Lane
Joined: Oct 2011
Posts: 59
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Most GM vehicles use what's called Passlock™ now. Instead of using a chipped key, (key with built in resistor) the ignition lock has a coded magnet built into the cylinder itself and passes over a hall effect sensor as you turn the ignition from LOCK to RUN. The sensor reads the code on the magnet and sends it to the BCM. If it's the correct code, the BCM sends a signal to the ECM, telling it to enable fuel and spark when you start the vehicle.
The CAN bus is really not that involved in the Passlock™ system.
The CAN bus is really not that involved in the Passlock™ system.
Thread Starter
Teching In
Joined: Nov 2012
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So I am talking about the newer Gen IV stuff. I have my starter wired in a more traditional method so Passlock isn't really my concern.
More what I am wondering is, if I used a BCM that isn't VIN matched to my car would it still work for functions like cruise control and transmission functions?
More what I am wondering is, if I used a BCM that isn't VIN matched to my car would it still work for functions like cruise control and transmission functions?
Staging Lane
Joined: Apr 2007
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Depending on the model your components are from the vins must match. You can reprogram the bcm with a tech2. Some models use a pim(powertrain interface module) like gto's. It must be relearned and synced to the pcm and bcm or wierd things happen. What exact year and model components are you using?
So I am talking about the newer Gen IV stuff. I have my starter wired in a more traditional method so Passlock isn't really my concern.
More what I am wondering is, if I used a BCM that isn't VIN matched to my car would it still work for functions like cruise control and transmission functions?
More what I am wondering is, if I used a BCM that isn't VIN matched to my car would it still work for functions like cruise control and transmission functions?
passlock will shut down the engine. you can tune this out though.
you need all the components(depending on your application), and if the VINs match its a plus. If they don't you can go to a dealer or a well equipped indy and they can sync everything.
I do not think cruise will work without the vins matching. cruise is low on the pecking chart and many other functions must align before the computers will cruise.
Thread Starter
Teching In
Joined: Nov 2012
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I am currently running a 2009 silverado ECM and TCM. This is installed in the car and working. Have been driving the car for almost a year this way.
I recently got a BCM off e-bay and am curiuos if it will work with my setup. I am not sure what the BCM came out of but the add claimed to work for my vintage of silverado. My local dealership has gone out of there way to not be helpful on this project, so I am hoping a flash isn't required.
So the BCM won't go into normal operation unless it talks to the ECM and verify's the VIN is correct? Or the ECM won't listen to the BCM unless it verifies the VIN? OR something different from both those scenarios all together?
Thanks,
Pat
I recently got a BCM off e-bay and am curiuos if it will work with my setup. I am not sure what the BCM came out of but the add claimed to work for my vintage of silverado. My local dealership has gone out of there way to not be helpful on this project, so I am hoping a flash isn't required.
So the BCM won't go into normal operation unless it talks to the ECM and verify's the VIN is correct? Or the ECM won't listen to the BCM unless it verifies the VIN? OR something different from both those scenarios all together?
Thanks,
Pat
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Teching In
Joined: Mar 2014
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From: Galveston, TX
Any update on this? Im about to be in a similar situation.
I am currently running a 2009 silverado ECM and TCM. This is installed in the car and working. Have been driving the car for almost a year this way.
I recently got a BCM off e-bay and am curiuos if it will work with my setup. I am not sure what the BCM came out of but the add claimed to work for my vintage of silverado. My local dealership has gone out of there way to not be helpful on this project, so I am hoping a flash isn't required.
So the BCM won't go into normal operation unless it talks to the ECM and verify's the VIN is correct? Or the ECM won't listen to the BCM unless it verifies the VIN? OR something different from both those scenarios all together?
Thanks,
Pat
I recently got a BCM off e-bay and am curiuos if it will work with my setup. I am not sure what the BCM came out of but the add claimed to work for my vintage of silverado. My local dealership has gone out of there way to not be helpful on this project, so I am hoping a flash isn't required.
So the BCM won't go into normal operation unless it talks to the ECM and verify's the VIN is correct? Or the ECM won't listen to the BCM unless it verifies the VIN? OR something different from both those scenarios all together?
Thanks,
Pat
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I just had a BCM go bad in my daughters Saturn Vue. I am no expert by any means. I did find out that in that particular model, it stores the mileage, and can not be changed with a Tech2. I was told there is no vin in that. I do know that you can do the 3 10 min security releans on that type to get the vehicle to start. As far as cruise, ABS, fog lamps etc, they can be turned on or off by a Tech2. I did learn that the main part# on the top of the BCM needed to match in order to work at all. If I would have found a used BCM with the same options the only thing that would have needed programing to my knowledge would have been the remote key fob.
I don't know if any of that helps at all, but I figure any knowledge is better than none.
I don't know if any of that helps at all, but I figure any knowledge is better than none.
as the years got newer so did the BCMs complexity.
as far as I know the 09 BCM is not reflashable(by normal means)
so the VIN and options are burned into it at initial startup
A reman will be a blank slate that can be customized if you find a willing dealer.
as far as I know the 09 BCM is not reflashable(by normal means)
so the VIN and options are burned into it at initial startup
A reman will be a blank slate that can be customized if you find a willing dealer.
