Diagnostic Trouble Codes

[suwisa]

I use Freematics ONE to develop my app using Arduino. I try to read DTC Codes, the code is like this:

Code: Select all

char buffer[64];
  write("0101\r");
  int bytesReceived = receive(buffer,sizeof(buffer),1000);
  buffer[bytesReceived+1] = 0; 
  if (bytesReceived > 0) {
    Serial.println(buffer);
  }

bytesReceived is greater than zero and buffer is "$OBD41 01 81 04 00 00"

Why the first byte response start with "$OBD"?
Do you have sample code for retrieving DTC Codes?

Thanks