Determining baud rate with no traffic

[fbwarren]

I am trying to determine the baud rate of a network, but there's no traffic to listen to. I think this is because newer cars have a sort of gateway preventing listening in on traffic. Is there a way to try sending messages at various rates and listening for errors/responses to determine the correct speed? Here's what I've tried:

uint32_t beginAutoSpeedActive(MCP2517FD *network)
{
  uint32_t canspeed = 0;
  uint32_t bauds [2] = {125,500};

  CAN_FRAME msg;
  msg.id = 0x7ff;
  msg.length = 8;
  msg.extended = false;
  msg.rtr = false;
  msg.data.byte[0] = 0x01;
  msg.data.byte[1] = 0x02;
  msg.data.byte[2] = 0x03;
  msg.data.byte[3] = 0x04;
  msg.data.byte[4] = 0x05;
  msg.data.byte[5] = 0x06;
  msg.data.byte[6] = 0x07;
  msg.data.byte[7] = 0x08;

  for (int i = 0; i < 2; i++)
  {
    canspeed = bauds[i] * 1000;

    network->enable();
    network->begin(canspeed);
    network->watchFor();
    network->sendFrame(msg);
    
    bool error = false;
    unsigned long startTime = millis();
    
    while ((millis() - startTime) < 1000)
    {
      if (network->hasTXFault())
      { 
        error = true;
        network->Write16(ADDR_CiINT, 0);    // acknowledge interrupts/fault
        break;
      }
    }

    network->resetHardware();
    delay(500);
    network->disable();       // resetting hardware enables the network

    if (!error)
    {
      return canspeed;
    }
  }

  return 0;
}