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Thread: NEWB question. Anyone familiar with GMLAN. Please help!

  1. #31
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    heavymetal:
    Yes very handy! If I were to use my OEM radio in another vehicle which is not likely. But it is good knowledge to have.

    sshep1:
    My hunch is that the BCM (Body Control Module) is the central brain for everything you need. Without the Vin check you can get the radio working but the HVAC controls likely go to the BCM for it to control what it needs to to make the HVAC system work. It is not likely that it communicates directly to the HVAC brain. Your response from scosche confirms my original assumption that the radio was using the CAN bus to communicate the information to the HVAC brain.

    I would STRONGLY suggest getting the G8 manual as i listed above. It will help you decide if you REALLY want to install that OEM radio to do what you want. And for $10 plus shipping if it even saves you an hour of work it is well worth it. It may even tell you if the Controls talk directly to the brain or if they talk to the BCM which then talks to the HVAC brain.

    You have likely verified it is using the CAN network and can for sure verify that when you get a copy of the manual. The mentioned manual is a DVD copy of it but will contain everything in the printed version.

    Chances are that getting the BCM will NOT work for you. This is where an Arduino with the ODBII shield on it comes into play. The Arduino then runs a software program that mimics the BCM allowing you to add whatever modules you want to add to your car and allow them to get the information they need. With this it can also mimic response of any other module you need as well. Basically you are making an ODBII emulator to communicate with your modules to make them work correctly. The reason why the BCM won't likely work is because it will try to communicate with other modules that are not there. It will likely cause errors with the BCM and cause other issues possibly locking it up or severely delaying its actions as it times out trying to communicate with other systems. It MAY work even with the numerous error codes it will throw but you won't know unless you try. Using an Arduino as an emulator works because you can program its responses and you won't throw any codes or have other issues you may have using a BCM without the modules connected. Using an Arduino you will need to learn how to program it unless you can find someone that has already done this. The program its self shouldn't be that big an issue since there IS an Arduino ODB II shield available. It should come with the software that allows you to talk to the CAN bus that you then modify to make work for your application.

    If you had a buddy that could rewrite the BCM program you could get around many of the issues but baring that the Arduino or similar type system is the way to get around the need of the BCM.

    Your biggest issue with getting the HVAC brain to work will be communicating with it. There really are only two ways to get the proper sequencing down. You need an operational vehicle that you can scan the codes from and then try those codes in the Arduino until you get it working properly. Or pay the thousands of dollars for a 1 year subscription and obtain the codes and information from GM. If you pay the money you will shorten your project time considerably since you will have the full information on how the CAN network works in your car. It would be cool if you could get more information from the scosche guys. They could possibly give you all of the information but since they likely obtained it from GM using the subscription I mentioned which contains a NDA they can not legally give you that information without violating their NDA.

    To give you an idea... With my truck I will sniff the codes I need then incorporate them into a small computer board likely running either and ARM or Propeller as the CPU. This computer will then act like it is the module that would normally do those commands and go from there. I expect and hope that the controls in my truck are similar to those in your car. I expect that I will find my HVAC controls end up sending CAN messages to the BCM and the BCM then coordinates with the HVAC brain to control the interior of my truck. If it is then I can sniff those commands and get to the point I understand them enough that I can remove my HVAC controls all together and use the computer to act in its place. Then I can make the controls automatic if I so desire even though my truck did not come with automatic HVAC controls. Hmm now you got me wanting to pull up my manual and look at its HVAC system.

  2. #32
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    One last note which warrants a separate message. You MAY be able to find another vehicle with a similar system to be able to sniff it instead of needing the exact same car. The G8 is an Australian import and is very similar to the GTO. I believe the Camaro is also on the same platform and the new Impala/Caprice is also. You MAY be able to find out if they use a similar system and use them to sniff the information you need. They may not be 100% but might be close enough to get you what you need. You may also be able to accomplish this by wiring in the BCM anyhow and sniffing the codes. You should be able to tell which codes to ignore and only pull the ones you need. Then you insert those into your Arduino and ditch the BCM when you get it working. I am guessing the BCM will be giving you fits otherwise and may not work consistently in your system. You may get lucky and hook it up and it works however and my suggestion of many hours be off.

  3. #33
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    redheadedrod: so I dint get teh manual you suggested. It will take for ever to get to me in Afghanistan. It did remind me that I had a subscription to the ALLDATAdiy.com site for teh G8 and here is what I found out.

    There is a module just for the HVAC p/n: 92191991

    Apparently according to teh wiring schematic there is nothing in between teh HVAC controls and the module, unless I am interpreting this wrong completely. Let me know if this diagram will help or if you will need more information.

    There are obviously several modules that interface wth the BCM. White auto media sales offers a BCM reprogramming option. I just hope that White can reprogram the BCM to meet my requirements. I am going to email him. He and I have emailed back and forth several times previous to this. If he can reprogram the BCM I should be able to use it in a standalone config just for teh radio/HVAC setup. (http://www.whiteautoandmedia.com/ind...mart&Itemid=54)
    Attached Images Attached Images  

  4. #34
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    Here is another diagram shopwin the connection between teh HVAc controls and the module.

    Also is another diagram showing the connection between the HVAC controls and the ECU to control the compressor. Do you think the compressor can be re routed so that the compressor is wired directly to the HVAC controls and doesnt go through the ECU?
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  5. #35
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    That ECM monitoring of A/C gas pressure is a concern in that the communication to the HVAC control module and the HVAC control is involved.

    I know it sends "shut down" commands in case of over/under pressure.

    YUK.

  6. #36
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    Your pictures are a little conflicting. The first picture and the second show the radio connected directly to the HVAC module with a data connection. The CAN databus being a different connection.

    The last picture makes it look like the radio and HVAC module connect to the databus and talk across that.

    Are they different schematics for different versions?

    Looks like at a minimum if you are lucky you should be able to get it up and running without the BCM.... But you won't have AC. Looks more like a connection to the ECM is needed than anything else. The BCM may talk to it if there is a car start module to turn on the controls. To ME that what those schematics seem to show. You likely could still use an Arduino programmed as a simulator to talk to your HVAC controls to get it to be fully functioning but you will want to make the Arduino talk to the A/C compressor to make sure the safeties are incorporated. You could make the HVAC module believe it is still connected in the original car this way. Still not getting away from the need to sniff the codes unless you can get them otherwise.

  7. #37
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    Name:  RAD1.jpg
Views: 188
Size:  26.2 KBName:  RAD 2 digital.jpg
Views: 195
Size:  28.7 KBAll the schematics are from the ALLDATAdiy.com website for the G8. These are the schematics for the radio as well, it seems to me that the only reason for the BCM connection is for the operation of the steering wheel controls, onstar, and the phone connection. Then again I really am not sure, not enough experience yet. One question I have that will show my experience level, or should I say inexperience level. What is the box with the opposing arrows that connects the controls to teh different modules. I was assuming it was a data connection and not the BCM. Am I even close? So taking into consideration the schematics for everything does this seem more likely to happen or am I still ****ing into the wind?

  8. #38
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    That box with arrows shows there is communication both ways.

  9. #39
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    Ok that makes sense.

    Well if the radio can be reprogrammed to be independent of the BCM and just function by itself, and the HVAC doesnet need to talk to the BCM but instead needs to communicate with the ECU. Then this should work right? Its easier to have the ECU programmed to be able to monitor pressures. OR is there somone who can build an Audrino unit for this application?

  10. #40
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    That makes it worse.

    The algo is probably monitoring engine speed at the very least, and looks like it is monitoring refrigerant pressure.

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