SeeedStudio CAN bus shield arduino ECU_Request - c++

Question

I have tried to make an ecuRequest which sends a PID to a can network and then receives a message. I got this idea from the demo sketch in this article http://skpang.co.uk/blog/archives/55. I've tried to mimic the ecu_req using the seeedstudio library found here https://github.com/Seeed-Studio/CAN_BUS_Shield. Below is what I have so far. The buffer gets filled when I connect it up to my car but it doesnt seem to be the right data.
char MCP_CAN::pidRequest(unsigned char pid, INT8U buf,float& engineData)
{
INT8U len = 8;
float engine_data;
uint8_t data[8];
data[0] = 0x02;
data[1] = 0x01;
data[2] = 0x0c;
data[3] = 0x00;
data[4] = 0x00;
data[5] = 0x00;
data[6] = 0x00;
data[7] = 0x00;
//uint8_t *ptr = data;
mcp2515_modifyRegister(MCP_CANCTRL, (1<<7)|(1<<6)|(1<<5), 0); //change mode_mask if doesnt work
if(sendMsgBuf(0x7DF, 1, 0, 8, data)==CAN_OK) {
delay(100);
if(checkReceive()==CAN_MSGAVAIL) {
if (readMsgBuf(&len, buf)==CAN_OK) {
//engine_data = ((buf[3]*256)+buf[4])/4;
Serial.println(buf[0]);
Serial.println(buf[1]);
Serial.println(buf[2]);
Serial.println(buf[3]);
Serial.println(buf[4]);
Serial.println(buf[5]);
Serial.println(buf[6]);
Serial.println(buf[7]);
return 0;
}
else{
return 1;
}
}
else{
return 2;
}
}
else{
return 3;
}

Answer 1

You only check one message, but there are many different messages on the bus, regardless of what you send.
You should either read every message until you get the one with the CAN ID you expect (probably CAN ID 0x7e8) or set an appropriate filter/mask in the MCP chip, so it will only send you relevant messages.