Arduino Sparkfun CAN BUS Shield Vehicle Speed

/*
This is for use with Sparkfun's CAN Bus Shield: https://www.sparkfun.com/products/10039
Library located in Sparkfun CAN Bus Shield Library on Github: https://github.com/sparkfun/SparkFun_CAN-Bus_Arduino_Library
*/

#include <Canbus.h>
#include <defaults.h>
#include <global.h>
#include <mcp2515.h>
#include <mcp2515_defs.h>

void setup() {
  Serial.begin(9600);
  Serial.println("CAN BUS Vehicle Speed");
  delay(1000);

  if(Canbus.init(CANSPEED_500))  //Initialise MCP2515 CAN controller at the specified speed
    Serial.println("CAN Init ok");
  else
    Serial.println("Can't init CAN");

  delay(1000);
}

void loop(){
//FIRST ---- Send PID Request for vehicle speed
tCAN message;
float engine_data;
char *buffer;

    message.id = 0x7DF; //PID REQUEST message.id =0x7DF
    message.header.rtr = 0;
    message.header.length = 8;
    message.data[0] = 0x02;
    message.data[1] = 0x01;
    message.data[2] = 0x0D; //vehicle speed PID
    message.data[3] = 0x00;
    message.data[4] = 0x00;
    message.data[5] = 0x00;
    message.data[6] = 0x00;
    message.data[7] = 0x00;

mcp2515_bit_modify(CANCTRL, (1<<REQOP2)|(1<<REQOP1)|(1<<REQOP0), 0);
mcp2515_send_message(&message);

delay(200); //delay 0.2 seconds, but may not be needed

//SECOND ---- Filter for PID REPLY with message.id =0x7E8 and message.data[2] =0x0D
//tCAN message;
if (mcp2515_check_message())
  {
    if (mcp2515_get_message(&message))
    {
    if(message.id == 0x7E8 and message.data[2] == 0x0D) //Filter
      {
        engine_data =  message.data[3];
        sprintf(buffer,"%d km ",(int) engine_data);
      }
    }
  }
  delay(1000);
}