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šŸš— OBD-II CAN Bus Car Scanner

Decode live engine data from any modern car using MCP2515 and OBD-II PIDs.

šŸ“‹ Overview

Every modern car (1996+ in the US, 2001+ in Europe) has an OBD-II port that exposes the CAN bus ā€” a robust automotive serial protocol. The MCP2515 is a standalone CAN controller that communicates via SPI with Arduino. By sending standard OBD-II Parameter IDs (PIDs), we can request engine RPM, vehicle speed, coolant temperature, throttle position, and read fault codes.

What you'll learn: CAN bus physical layer (CAN-H, CAN-L, differential signalling), MCP2515 SPI initialization and baud rate matching (500kbps for OBD-II), OBD-II request/response PID format, decoding multi-byte responses, and displaying data on TFT or OLED.

Estimated time: 2ā€“3 hours. Difficulty: ā­ā­ā­ā­ Advanced.

šŸ§© Components Needed

ComponentSpecificationQtyNotes
Arduino NanoATmega328P, 5V1Compact, easy to mount in car
MCP2515 CAN ModuleSPI, 16MHz crystal1CAN bus controller + TJA1050 transceiver
OBD-II Breakout ConnectorStandard 16-pin J19621Plugs into car dashboard port
0.96" OLED DisplayI2C SSD13061Compact dashboard display
Wires & Enclosure1 setMount near OBD port

šŸ“– Step-by-Step Tutorial

1

Wire MCP2515 to Arduino

MCP2515 VCC ā†’ 5V, GND ā†’ GND, CS ā†’ Pin 10, SI ā†’ Pin 11 (MOSI), SO ā†’ Pin 12 (MISO), SCK ā†’ Pin 13, INT ā†’ Pin 2. Note: Use 5V power, not 3.3V.
2

Connect to OBD-II Port

OBD-II Pin 6 = CAN-H, Pin 14 = CAN-L. Connect to MCP2515 CANH and CANL. OBD-II Pin 16 = 12V battery, Pin 4 = Chassis GND ā€” use a 12Vā†’5V regulator.
3

Install CAN Library

Install mcp_can by Cory Fowler from Library Manager. Initialize at 500kbps: CAN.begin(CAN_500KBPS).
4

Send OBD-II PID Requests

Send a CAN frame: ID=0x7DF (broadcast), DLC=8, Data=[0x02, 0x01, PID, 0x00, 0x00, 0x00, 0x00, 0x00]. The ECU responds on ID 0x7E8 with the value.
5

Decode Responses & Display

Parse the response byte(s) using the PID formula. RPM = (byte3 Ɨ 256 + byte4) / 4. Speed = byte3 km/h. Coolant temp = byte3 āˆ’ 40 Ā°C. Display on OLED.
šŸ’”
OBD-II PID support varies by car manufacturer and model year. Mode 01 (live data) PIDs are standardized, but not every ECU supports all of them. Always check if response[4] == requestedPID before decoding the value.

šŸ’» Code / Configuration

obd2_reader.ino
INO
// OBD-II CAN Bus Scanner - Volt X
#include <SPI.h>
#include <mcp_can.h>
#include <Wire.h>
#include <Adafruit_SSD1306.h>

MCP_CAN CAN(10); // CS on Pin 10
Adafruit_SSD1306 oled(128, 64, &Wire, -1);

// OBD-II PID codes (Mode 01)
#define PID_RPM       0x0C
#define PID_SPEED     0x0D
#define PID_COOLANT   0x05
#define PID_THROTTLE  0x11

void requestPID(byte pid) {
  byte msg[8] = {0x02, 0x01, pid, 0x00, 0x00, 0x00, 0x00, 0x00};
  CAN.sendMsgBuf(0x7DF, 0, 8, msg); // 0x7DF = OBD-II broadcast ID
}

int decodePID(byte pid, byte b3, byte b4) {
  switch (pid) {
    case PID_RPM:     return ((b3 * 256) + b4) / 4;
    case PID_SPEED:   return b3;
    case PID_COOLANT: return b3 - 40;

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