Page 1 of 2 12 LastLast
Results 1 to 20 of 22

Thread: Looking for info on the Can Bus

  1. #1
    Tuner in Training
    Join Date
    Jan 2019
    Posts
    15

    Looking for info on the Can Bus

    All,

    I have a 71 Firebird with a 2017 GMPP LT4 Crate Engine with manual transmission (TKX) and I am using the GMPP Controller package. Ihave an oddity with trying to get a Dakota Digital CRC-1000 cruise control to work. It gets it information from the Can bus. I have the Can wires from the cruise pinned to the bulkhead connector supplied with the GM harness that is parralelled off the back of the OBD2 port pins 6 and 14.

    Now here is the oddity, the cruise will function correctly as long as I have my MPVI2 plugged into the OBD2 port. I do not have to have my laptop plugged in and I have not set up stand alone logging.

    If I do not have the MPVI2 plugged in the cruise will not engage.

    If I start with the MPVI2 plugged in,get up to 55 mph, set the cruise, and it will engage for as long as I leave it plugged in. If while it is engaged engaged I pull the MPVI2 the cruise immediately shuts off.

    It's like the data is not availabe on the Bus unless the MPVI2 is plugged in.

    I'm pretty new at this stuff, and it took me a bit to figure out what did and did not allow the cruise to work. Everything I stated above has been tested multiple times so I believe there are no coincidences.

    Thanks,

    Stan

  2. #2
    Advanced Tuner
    Join Date
    Aug 2010
    Location
    Detroit, MI
    Posts
    932
    One tester present at a time please

  3. #3
    Tuner in Training
    Join Date
    Jan 2019
    Posts
    15
    Not exactly sure what you mean by that?. The cruise control only works when the MPVI2 is plugged in.

  4. #4
    Tuner in Training
    Join Date
    Oct 2021
    Posts
    46
    Starting simple key on engine off check resistance across the CAN bus 60 ohms is best 120 is possible.

    I assume all you have on the CAN is the PCM and Dakota Digital system.

    I have to admit this sounds interesting but assume you are not local.

  5. #5
    Tuner in Training
    Join Date
    Jan 2019
    Posts
    15
    It has 120 ohms.

    I think the fuel pump control module is on the bus also. But I?m not 100% l

    I was able to get a cheap Bluetooth dongle to make it work also. Had to pair my phone with it though. I assume the PCM isn?t broadcasting the data until something polls for it.

    Without my phone paired it doesn?t work. So it is not just a MPVI2 thing.

    Dakota Digital confirmed the cruise doesn?t poll, just sniffs.

    I?m in Toledo Illinois

  6. #6
    Tuner in Training
    Join Date
    Oct 2021
    Posts
    46
    It should have another terminator on the bus but that is some of the beauty of CAN, even a poorly configured bus will often work.

    I am odd and it would be honestly fun to me to log the can with and without you MPVI and Blue Tooth dongle to see what messages are changing.
    You are not close enough for me to jump in and I wish you luck with it.

    Even though you termination isn't right that isn't likely the issue.

    It doesn't sound like the information from Dakota is entirely accurate either. information isn't always broadcast without polling and it could be the simple act of the dongle or other cheap scan tool is initiating the initial messages required Dakota system.

    All I see from Dakota is "Works with 2008 and newer GM CAN bus engine/drivetrain packages with US SAE code" If you did log the CAN it would be nice to to know what messages in particular the system is looking for, again it seems your secondary devices are initiating that communication to get those messages broadcast.

  7. #7
    Tuner in Training
    Join Date
    Jan 2019
    Posts
    15
    Any suggestions on how I can log the Can?

  8. #8
    Tuner in Training
    Join Date
    Oct 2021
    Posts
    46
    There are cheap tools available but sometimes the software then kind of sucks. Maybe try asking for help logging CAN on FB, maybe able to find someone local. They don't need to be car guys just people who play in software and CAN. dr,mike on this forum maybe of more assistance but I know he is also in mid move right now. I have been around CAN for many years but only actively learning it the past year.

    We use the sysworxx-usb-can a lot at work but I prefer the Kvaser products and software. I have not tried the inexpensive ones from Amazon.

  9. #9
    Senior Tuner TheMechanic's Avatar
    Join Date
    Jan 2014
    Location
    SoCal
    Posts
    1,557
    120 ohms. Missing terminating resistor that is about 5 inches back on a vehicle. Since you don't have anything on the CAN line it would run fine without one. Now that you need CAN, you need the term-resistor.
    https://www.summitracing.com/parts/ado-88988999

  10. #10
    Tuner in Training
    Join Date
    Jan 2019
    Posts
    15
    Can anyone confirm the factory Fuel Pump Control Module is on the Can?

    Also exactly where do I add the resistor? 6? from the Cruise Module or 6? from the OBD2 port?

    Assuming it needs a 120ohm resistor across the high and low can?

    Thanks
    Last edited by stan65; 05-04-2022 at 03:05 PM.

  11. #11
    Tuning Addict blindsquirrel's Avatar
    Join Date
    Apr 2017
    Location
    Meridian MS
    Posts
    7,583
    Draw out a wiring diagram of your current system, hard to visualize these things without a diagram. You can then compare to a factory stock diagram, and see how it needs to be configured to still work without all the original modules in the chain.

  12. #12

  13. #13
    Tuner in Training
    Join Date
    Jan 2019
    Posts
    15
    I do not have prints. Gm doesn?t supply schematics with their controller package. They do include the pinout of the ECM.

    I believe the Fuel pump control module is on the blue connector, pins 36 and 37

    I believe the OBD2 is connected to the blue connector, pins 39 and 40

    It somewhat matches the drawing on the left with the OBD2 port paralleling the bus.
    My harness has a ?bulkhead? connector in the location of the TCM in the drawing. That is where I landed the cruise control LAN wires.

  14. #14
    Tuning Addict blindsquirrel's Avatar
    Join Date
    Apr 2017
    Location
    Meridian MS
    Posts
    7,583
    Of course GM didn't supply a diagram, and even if they had it wouldn't be accurate now as you changed it by adding stuff to the bus.

    Pencil, paper, DVOM.

  15. #15
    Tuner in Training
    Join Date
    Jan 2019
    Posts
    15
    BUS.jpg

    Here is what I have. There are no terminating resistors at the OBD2 or Cruise.
    I have 120-ohm resistors that I can install.
    Last edited by stan65; 05-04-2022 at 05:57 PM.

  16. #16
    Tuner in Training
    Join Date
    Oct 2021
    Posts
    46
    The ECU is terminated and your harness isn't and nothing on the bus is either and this is common. The ECU is on one end 120 ohms and and you should have another terminator on the far end but really on a small can bus with almost nothing on it it should work with just the ECM. in a perfect world another 120 ohms across the can at the farthest end of the can harness would be best. Ni ether your MPVI or you blue tooth dongle have termination so even though your termination is incorrect I don't feel it it the cause but you can just hang a 120 ohm resistor across the can and see it your cruise works. put the resistor as close the Dakota module as possible just assuming the likely farthest from the ECM. Some PCM's wont broadcast unless they are polled, I am thinking you MPVI or dongle are initiating. Without a schematic and or CAN logs it is is guessing. For those here that know is the DBW sistem analog or is that CAN also?

  17. #17
    Tuner in Training
    Join Date
    Oct 2021
    Posts
    46
    Quote Originally Posted by stan65 View Post
    BUS.jpg

    Here is what I have. There are no terminating resistors at the OBD2 or Cruise.
    I have 120-ohm resistors that I can install.
    For termination you just need a 120 ohm resistor across the bus on the farthest end. The if you check across the bus you will show 60 ohms.

  18. #18
    Tuner in Training
    Join Date
    Jan 2019
    Posts
    15
    I will try adding the termination resister at the cruise. It is the farthest from the ECM and is exactly like the drawing. It is pouring down rain here, so I won't be able to try it till the weather clears up.

    And just to be clear, the cruise WORKS when the dongles are hooked up.

    Lastly, I appreciate every body's patience.

    I updated the drawing to more closely reflect the actual wire connection locations.

    BUS.jpg
    Last edited by stan65; 05-04-2022 at 06:11 PM.

  19. #19
    Tuner in Training
    Join Date
    Oct 2021
    Posts
    46
    Quote Originally Posted by stan65 View Post

    And just to be clear, the cruise WORKS when the dongles are hooked up.


    BUS.jpg
    The resistor will make you CAN bus "more" correct but I feel this statement of yours carries a lot of value. In my quest to learn CAN I have found some ECU's don't speak unless spoken too. If the Dakota is passively listening as suggested I think you are just missing an imitating message. I also must add I am not a software person I am just a person learning and using can and my opinions are based of what you have told me and what I have experienced.

    I hope in time we can help you though this.

  20. #20
    Tuner in Training
    Join Date
    Jan 2019
    Posts
    15
    Thanks for all the replies....

    I will try a few things once the roads dry up. hopefully this weekend.

    On my list,

    Try 120-ohm terminating resistor at cruise end of network. (Will probably leave on for a more robust network if it doesn't cause any issues no matter what the solution is)

    Have purchased a Dakota Digital BIM-01-2 OBD-II/CAN Interface module. It is supposed to poll the ECM for data for their gauges even if the gauges aren't hooked up. It is supposed to arrive Friday.

    I basically think the I need to add a device that will poll the PCM for data if the Terminating resistor doesn't work. Just need to figure out what device is the right device. Thinking out loud, "can I hang a TCM or BCM on the Bus without having anything else hooked to it and make it work?"

    I will update the post after testing.

    Once again thanks all!
    Last edited by stan65; 05-06-2022 at 08:25 PM.