https://docs.macchina.cc/projects/mini-project-tutorials/a0-can-vehicle-data

A0_VehicleData.ino

#include <esp32_can.h>

uint8_t codes[4] = {5, 0xB, 0xC, 0xD};
int idx = 0;
uint32_t tick = 0;

const int led_pin = 13;

char msg_buf[10];
int led_state = 0;

int ledState = LOW;             // ledState used to set the LED
unsigned long previousMillis = 0;        // will store last time LED was updated
const long interval = 1000;           // interval at which to blink (milliseconds)

void setup()
{
  pinMode(led_pin, OUTPUT);
  digitalWrite(led_pin, LOW);
  
  // Start Serial port
  Serial.begin(115200);
  
  CAN0.setCANPins(GPIO_NUM_4, GPIO_NUM_5);
  CAN0.begin(500000);
  Serial.println("Ready ...!");
  
  int filter;
  //extended
  for (filter = 0; filter < 3; filter++)
  {
    Can0.setRXFilter(filter, 0, 0, false);
  }
}

void loop()
{
  CAN_FRAME incoming;
  
  if (Can0.available() > 0)
  {
    Can0.read(incoming);
    if (incoming.id > 0x7DF && incoming.id < 0x7F0)
    {
      processPID(incoming);
    }
  }
  
  static unsigned long l = 0;
  unsigned long t = millis();
  
  if ((t - l) > 50)
  {
    sendPIDRequest(0x7DF, 0xC);
    sendPIDRequest(0x7DF, 0xD);
    sendPIDRequest(0x7DF, 5);
    
    l = t;
  }
}

void sendPIDRequest(uint32_t id, uint8_t PID)
{
  CAN_FRAME frame;
  frame.id = id;
  frame.extended = 0;
  frame.length = 8;
  
  for (int i = 0; i < 8; i++)
    frame.data.bytes[i] = 0xAA;
  
  frame.data.bytes[0] = 2; //2 more bytes to follow
  frame.data.bytes[1] = 1;
  frame.data.bytes[2] = PID;
  Can0.sendFrame(frame);
}

int lastTemp=-1;
float lastpsi=-1;
int lastRPM=-1;
int lastMPH=-1;

void processPID(CAN_FRAME &frame)
{
  int temperature;
  float psi;
  int RPM;
  int MPH;

  if (frame.data.bytes[1] != 0x41)
    return; //not anything we're interested in then
  
  switch (frame.data.bytes[2])
  {
    case 5:
      temperature = frame.data.bytes[3] - 40;
      if (temperature!=lastTemp)
      {
        Serial.print("Coolant temperature (C): ");
        Serial.println(temperature);
        lastTemp=temperature;
      }
    break;
    
    case 0xB:
      psi = frame.data.bytes[3] * 0.145038; //kPA to PSI
      psi = psi - 14.8;
      //psi = psi * 100;
      if (psi!=lastpsi)
      {
        Serial.print("Manifold abs pressure (psi): ");
        Serial.println(psi);
        lastpsi=psi;
      }
    break;
    
    case 0xC:
      RPM = ((frame.data.bytes[3] * 256) + frame.data.bytes[4]) / 4;
      if (RPM!=lastRPM)
      {
        Serial.print("Engine RPM: ");
        Serial.println(RPM);
        sprintf(msg_buf, "%d", RPM);
        lastRPM=RPM;
      }
    break;
    
    case 0xD:
      MPH = frame.data.bytes[3] * 0.621371;
      if (MPH!=lastMPH)
      {
        Serial.print("Vehicle Speed (MPH): ");
        Serial.println(MPH);
        lastMPH=MPH;
      }
    break;
  }
}