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  • Looking for info on GM Class 2 Dash Control

    I am trying to control a GM dash that uses class 2 serial data (J1850 VPW), to control the secondary gauges. I am looking for the control PIDs that are used to command these gauges. Or does the dash query the PCM repeatedly? I am also looking for any info on controlling the DIC on the dash. It is a 98 Corvette dash.

  • #2
    Originally posted by matthud View Post
    I am trying to control a GM dash that uses class 2 serial data (J1850 VPW), to control the secondary gauges. I am looking for the control PIDs that are used to command these gauges. Or does the dash query the PCM repeatedly? I am also looking for any info on controlling the DIC on the dash. It is a 98 Corvette dash.
    I don't know about a '98 Corvette, but on my '01 Chevy, the dash mostly just listens for periodic broadcasts. You can see them with an OBD-II interface if you have one that can just passively monitor. I've taken control of my ECT gauge by reading all traffic headed to the dash module, then passing on some packets with the contents modified.

    I'm not sure how much repurposing can really be done with the D.I.C. button, etc. I've seen some after market stuff for things like exhaust control on Corvettes, but generally they wire into an unused 'accessory connection' on the module.

    Good Luck
    -jjf

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    • #3
      Originally posted by jfitzpat View Post
      I don't know about a '98 Corvette, but on my '01 Chevy, the dash mostly just listens for periodic broadcasts. You can see them with an OBD-II interface if you have one that can just passively monitor. I've taken control of my ECT gauge by reading all traffic headed to the dash module, then passing on some packets with the contents modified.

      I'm not sure how much repurposing can really be done with the D.I.C. button, etc. I've seen some after market stuff for things like exhaust control on Corvettes, but generally they wire into an unused 'accessory connection' on the module.

      Good Luck
      -jjf
      Ok, thats exactly what I want to do, control the gauges with the serial data.

      I want to see about putting messages into the DIC display, not re-purpose the button.

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      • #4
        Originally posted by jfitzpat View Post
        I don't know about a '98 Corvette, but on my '01 Chevy, the dash mostly just listens for periodic broadcasts. You can see them with an OBD-II interface if you have one that can just passively monitor. I've taken control of my ECT gauge by reading all traffic headed to the dash module, then passing on some packets with the contents modified.

        I'm not sure how much repurposing can really be done with the D.I.C. button, etc. I've seen some after market stuff for things like exhaust control on Corvettes, but generally they wire into an unused 'accessory connection' on the module.

        Good Luck
        -jjf
        Thats exactly what I am trying to do, control the dash gauges from a microcontroller or PC. Would you happen to have any of the commands necessary to talk to the dash(IPC).

        I was looking into changing the messages on the DIC display, not changing the button's function.

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        • #5
          Originally posted by matthud View Post
          Thats exactly what I am trying to do, control the dash gauges from a microcontroller or PC. Would you happen to have any of the commands necessary to talk to the dash(IPC).

          I was looking into changing the messages on the DIC display, not changing the button's function.
          I would do what Joe did, and sniff the bus to see what's there. On OBDLink, the command would be ATMA or STMA. Record a log, and post it here -- we'll help you make sense of it.

          Vitaliy
          OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
          Need to look up a diagnostic trouble code? Try the most up-to-date, free DTCsearch.com!

          You cannot send me a private message using this forum. Use my email instead: vitaliy[@]scantool.net.

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          • #6
            I do not have a vehicle to sniff on. I am putting a gauge cluster in a project car with a non GM PCM.

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            • #7
              Originally posted by matthud View Post
              I do not have a vehicle to sniff on. I am putting a gauge cluster in a project car with a non GM PCM.
              Well, you're out of luck then.

              Seriously though, it would be next to impossible for you to get the information you are after through any official sources due to copyright restrictions. Reverse engineering is by far the cheapest way to get it.

              Vitaliy
              OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
              Need to look up a diagnostic trouble code? Try the most up-to-date, free DTCsearch.com!

              You cannot send me a private message using this forum. Use my email instead: vitaliy[@]scantool.net.

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              • #8
                Originally posted by matthud View Post
                I do not have a vehicle to sniff on. I am putting a gauge cluster in a project car with a non GM PCM.
                I could dig up the packets that I intercepted for my test with my Chevy, but I'm not sure that would really help. It would be much easier to monitor the panel under proper operation on a working vehicle to get what you need.

                The problem is that GMLAN has a flexible formatting structure, so my packets may well not match yours at all.

                As far as changing the messages, I'm not sure that is possible. On my '01 Chevy, the messages pop up in response to some broadcasts, but the packets are typically 4-5 bytes, an error code, not the text (or image) to display.

                Sorry I couldn't be of more help.
                -jjf

                Comment


                • #9
                  Originally posted by jfitzpat View Post
                  I could dig up the packets that I intercepted for my test with my Chevy, but I'm not sure that would really help. It would be much easier to monitor the panel under proper operation on a working vehicle to get what you need.

                  The problem is that GMLAN has a flexible formatting structure, so my packets may well not match yours at all.

                  As far as changing the messages, I'm not sure that is possible. On my '01 Chevy, the messages pop up in response to some broadcasts, but the packets are typically 4-5 bytes, an error code, not the text (or image) to display.

                  Sorry I couldn't be of more help.
                  -jjf
                  If you could send me what you found for your Chevy dash, it might give me a starting point.

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                  • #10
                    Can anyone decode this message for me:
                    CC 10 60 19 12 FF FF 3E

                    I know about the header and the crc, so I guess the 19 12 FF FF is what I need to know. I have an elm interface and the dash. I am able to read some messages from the dash, and this is a request from the dash to the pcm and I need to figure out what it is sending.

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                    • #11
                      Hm, mode 19 is conspicuously missing from SAE J2190. They just skip over it, with no explanation.
                      OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
                      Need to look up a diagnostic trouble code? Try the most up-to-date, free DTCsearch.com!

                      You cannot send me a private message using this forum. Use my email instead: vitaliy[@]scantool.net.

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                      • #12
                        I figured this was one of the GM proprietary messages, and not one of the SAE standards.

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                        • #13
                          I was able to find the message formats in the SAE J2178 books, and I am able to command the fuel level, oil level and water temp. But about 5 seconds after I command it, the gauges go back to the failsafe position. This is on a dash that is not connected to the pcm or any other serial 2 device. I believe its because the gauge cluster knows there is no pcm present, and this lack of comm causes it to reset the position. Does anyone know of a way to emulate enough of the pcm messages to the gauge cluster to trick it into thinking it is there?

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