ELMduino

This is a simple yet powerful library to effortlessly interface your Arduino with an ELM327 OBD-II scanner. With this library, you can query any and all OBD-II supported PIDs to collect a wide variety of car data (i.e. speed, rpm, engine temp, etc). Also, you can use ELMduino to view and clear your car's trouble codes - no need ot go to AutoZone anymore!

Example Project:

Install:

Install ELMduino using the Arduino IDE's Libraries Manager (search "ELMduino.h")

Note:

If you're having difficulty in connecting/keeping connection to your ELM327, try using 38400 baud instead of 115200. If you still have trouble, try all other possible bauds. Lastly, if using BluetoothSerial on an ESP32, try using the ELM327's MAC address instead of the device name "OBDII" and remove paired devices using this sketch.

Concept of Execution

The library is non-blocking. This means when you query a PID e.g. myELM327.rpm(), the code does not wait around for the response, which would block your other code in the main loop from executing. With ELMDuino, your main loop can continue do other tasks. To make this work, you need to repeatedly call the PID query function and check the non-blocking receive state (myELM327.nb_rx_state) until it is equal to ELM_SUCCESS. If the status is not ELM_SUCCESS, the library could still be waiting for a response to be received. This is indicated by myELM327.nb_rx_state being equal to ELM_GETTING_MSG. If the status is not equal to either of these values (ELM_SUCCESS or ELM_GETTING_MSG), it indicates an error has occurred. You can call myELM327.printError() to check what the problem was. See the simple example below which queries the engine speed in RPM.

Just to be clear, do not try to query more than one PID at a time. You must wait for the current PID query to complete before starting the next one.

Example Code:

#include <SoftwareSerial.h>
#include "ELMduino.h"


SoftwareSerial mySerial(2, 3); // RX, TX
ELM327 myELM327;


uint32_t rpm = 0;


void setup()
{
  Serial.begin(115200);
  mySerial.begin(115200);
  myELM327.begin(mySerial, true, 2000);
}


void loop()
{
  float tempRPM = myELM327.rpm();

  if (myELM327.nb_rx_state == ELM_SUCCESS)
  {
    rpm = (uint32_t)tempRPM;
    Serial.print("RPM: "); Serial.println(rpm);
  }
  else if (myELM327.nb_rx_state != ELM_GETTING_MSG)
    myELM327.printError();
}

List of Supported OBD PID Processing Functions:

uint32_t supportedPIDs_1_20();

uint32_t monitorStatus();
uint16_t freezeDTC();
uint16_t fuelSystemStatus();
float engineLoad();
float engineCoolantTemp();
float shortTermFuelTrimBank_1();
float longTermFuelTrimBank_1();
float shortTermFuelTrimBank_2();
float longTermFuelTrimBank_2();
float fuelPressure();
uint8_t manifoldPressure();
float rpm();
int32_t kph();
float mph();
float timingAdvance();
float intakeAirTemp();
float mafRate();
float throttle();
uint8_t commandedSecAirStatus();
uint8_t oxygenSensorsPresent_2banks();
uint8_t obdStandards();
uint8_t oxygenSensorsPresent_4banks();
bool auxInputStatus();
uint16_t runTime();


uint32_t supportedPIDs_21_40();

uint16_t distTravelWithMIL();
float fuelRailPressure();
float fuelRailGuagePressure();
float commandedEGR();
float egrError();
float commandedEvapPurge();
float fuelLevel();
uint8_t warmUpsSinceCodesCleared();
uint16_t distSinceCodesCleared();
float evapSysVapPressure();
uint8_t absBaroPressure();
float catTempB1S1();
float catTempB2S1();
float catTempB1S2();
float catTempB2S2();


uint32_t supportedPIDs_41_60();

uint32_t monitorDriveCycleStatus();
float ctrlModVoltage();
float absLoad();
float commandedAirFuelRatio();
float relativeThrottle();
float ambientAirTemp();
float absThrottlePosB();
float absThrottlePosC();
float absThrottlePosD();
float absThrottlePosE();
float absThrottlePosF();
float commandedThrottleActuator();
uint16_t timeRunWithMIL();
uint16_t timeSinceCodesCleared();
float maxMafRate();
uint8_t fuelType();
float ethonolPercent();
float absEvapSysVapPressure();
float evapSysVapPressure2();
float absFuelRailPressure();
float relativePedalPos();
float hybridBatLife();
float oilTemp();
float fuelInjectTiming();
float fuelRate();
uint8_t emissionRqmts();


uint32_t supportedPIDs_61_80();

float demandedTorque();
float torque();
uint16_t referenceTorque();
uint16_t auxSupported();

Other commands

float batteryVoltage(void); // Gets vehicle battery voltage
int8_t get_vin_blocking(char vin[]); // Gets Vehicle Identification Number (VIN)

List of OBD Protocols:

const char AUTOMATIC                  = '0';
const char SAE_J1850_PWM_41_KBAUD     = '1';
const char SAE_J1850_PWM_10_KBAUD     = '2';
const char ISO_9141_5_BAUD_INIT       = '3';
const char ISO_14230_5_BAUD_INIT      = '4';
const char ISO_14230_FAST_INIT        = '5';
const char ISO_15765_11_BIT_500_KBAUD = '6';
const char ISO_15765_29_BIT_500_KBAUD = '7';
const char ISO_15765_11_BIT_250_KBAUD = '8';
const char ISO_15765_29_BIT_250_KBAUD = '9';
const char SAE_J1939_29_BIT_250_KBAUD = 'A';
const char USER_1_CAN                 = 'B';
const char USER_2_CAN                 = 'C';

List of standard PIDs:

const uint8_t SUPPORTED_PIDS_1_20              = 0;   // 0x00 - bit encoded
const uint8_t MONITOR_STATUS_SINCE_DTC_CLEARED = 1;   // 0x01 - bit encoded
const uint8_t FREEZE_DTC                       = 2;   // 0x02 -
const uint8_t FUEL_SYSTEM_STATUS               = 3;   // 0x03 - bit encoded
const uint8_t ENGINE_LOAD                      = 4;   // 0x04 - %
const uint8_t ENGINE_COOLANT_TEMP              = 5;   // 0x05 - °C
const uint8_t SHORT_TERM_FUEL_TRIM_BANK_1      = 6;   // 0x06 - %
const uint8_t LONG_TERM_FUEL_TRIM_BANK_1       = 7;   // 0x07 - %
const uint8_t SHORT_TERM_FUEL_TRIM_BANK_2      = 8;   // 0x08 - %
const uint8_t LONG_TERM_FUEL_TRIM_BANK_2       = 9;   // 0x09 - %
const uint8_t FUEL_PRESSURE                    = 10;  // 0x0A - kPa
const uint8_t INTAKE_MANIFOLD_ABS_PRESSURE     = 11;  // 0x0B - kPa
const uint8_t ENGINE_RPM                       = 12;  // 0x0C - rpm
const uint8_t VEHICLE_SPEED                    = 13;  // 0x0D - km/h
const uint8_t TIMING_ADVANCE                   = 14;  // 0x0E - ° before TDC
const uint8_t INTAKE_AIR_TEMP                  = 15;  // 0x0F - °C
const uint8_t MAF_FLOW_RATE                    = 16;  // 0x10 - g/s
const uint8_t THROTTLE_POSITION                = 17;  // 0x11 - %
const uint8_t COMMANDED_SECONDARY_AIR_STATUS   = 18;  // 0x12 - bit encoded
const uint8_t OXYGEN_SENSORS_PRESENT_2_BANKS   = 19;  // 0x13 - bit encoded
const uint8_t OXYGEN_SENSOR_1_A                = 20;  // 0x14 - V %
const uint8_t OXYGEN_SENSOR_2_A                = 21;  // 0x15 - V %
const uint8_t OXYGEN_SENSOR_3_A                = 22;  // 0x16 - V %
const uint8_t OXYGEN_SENSOR_4_A                = 23;  // 0x17 - V %
const uint8_t OXYGEN_SENSOR_5_A                = 24;  // 0x18 - V %
const uint8_t OXYGEN_SENSOR_6_A                = 25;  // 0x19 - V %
const uint8_t OXYGEN_SENSOR_7_A                = 26;  // 0x1A - V %
const uint8_t OXYGEN_SENSOR_8_A                = 27;  // 0x1B - V %
const uint8_t OBD_STANDARDS                    = 28;  // 0x1C - bit encoded
const uint8_t OXYGEN_SENSORS_PRESENT_4_BANKS   = 29;  // 0x1D - bit encoded
const uint8_t AUX_INPUT_STATUS                 = 30;  // 0x1E - bit encoded
const uint8_t RUN_TIME_SINCE_ENGINE_START      = 31;  // 0x1F - sec

const uint8_t SUPPORTED_PIDS_21_40             = 32;  // 0x20 - bit encoded
const uint8_t DISTANCE_TRAVELED_WITH_MIL_ON    = 33;  // 0x21 - km
const uint8_t FUEL_RAIL_PRESSURE               = 34;  // 0x22 - kPa
const uint8_t FUEL_RAIL_GUAGE_PRESSURE         = 35;  // 0x23 - kPa
const uint8_t OXYGEN_SENSOR_1_B                = 36;  // 0x24 - ratio V
const uint8_t OXYGEN_SENSOR_2_B                = 37;  // 0x25 - ratio V
const uint8_t OXYGEN_SENSOR_3_B                = 38;  // 0x26 - ratio V
const uint8_t OXYGEN_SENSOR_4_B                = 39;  // 0x27 - ratio V
const uint8_t OXYGEN_SENSOR_5_B                = 40;  // 0x28 - ratio V
const uint8_t OXYGEN_SENSOR_6_B                = 41;  // 0x29 - ratio V
const uint8_t OXYGEN_SENSOR_7_B                = 42;  // 0x2A - ratio V
const uint8_t OXYGEN_SENSOR_8_B                = 43;  // 0x2B - ratio V
const uint8_t COMMANDED_EGR                    = 44;  // 0x2C - %
const uint8_t EGR_ERROR                        = 45;  // 0x2D - %
const uint8_t COMMANDED_EVAPORATIVE_PURGE      = 46;  // 0x2E - %
const uint8_t FUEL_TANK_LEVEL_INPUT            = 47;  // 0x2F - %
const uint8_t WARM_UPS_SINCE_CODES_CLEARED     = 48;  // 0x30 - count
const uint8_t DIST_TRAV_SINCE_CODES_CLEARED    = 49;  // 0x31 - km
const uint8_t EVAP_SYSTEM_VAPOR_PRESSURE       = 50;  // 0x32 - Pa
const uint8_t ABS_BAROMETRIC_PRESSURE          = 51;  // 0x33 - kPa
const uint8_t OXYGEN_SENSOR_1_C                = 52;  // 0x34 - ratio mA
const uint8_t OXYGEN_SENSOR_2_C                = 53;  // 0x35 - ratio mA
const uint8_t OXYGEN_SENSOR_3_C                = 54;  // 0x36 - ratio mA
const uint8_t OXYGEN_SENSOR_4_C                = 55;  // 0x37 - ratio mA
const uint8_t OXYGEN_SENSOR_5_C                = 56;  // 0x38 - ratio mA
const uint8_t OXYGEN_SENSOR_6_C                = 57;  // 0x39 - ratio mA
const uint8_t OXYGEN_SENSOR_7_C                = 58;  // 0x3A - ratio mA
const uint8_t OXYGEN_SENSOR_8_C                = 59;  // 0x3B - ratio mA
const uint8_t CATALYST_TEMP_BANK_1_SENSOR_1    = 60;  // 0x3C - °C
const uint8_t CATALYST_TEMP_BANK_2_SENSOR_1    = 61;  // 0x3D - °C
const uint8_t CATALYST_TEMP_BANK_1_SENSOR_2    = 62;  // 0x3E - °C
const uint8_t CATALYST_TEMP_BANK_2_SENSOR_2    = 63;  // 0x3F - °C

const uint8_t SUPPORTED_PIDS_41_60             = 64;  // 0x40 - bit encoded
const uint8_t MONITOR_STATUS_THIS_DRIVE_CYCLE  = 65;  // 0x41 - bit encoded
const uint8_t CONTROL_MODULE_VOLTAGE           = 66;  // 0x42 - V
const uint8_t ABS_LOAD_VALUE                   = 67;  // 0x43 - %
const uint8_t FUEL_AIR_COMMANDED_EQUIV_RATIO   = 68;  // 0x44 - ratio
const uint8_t RELATIVE_THROTTLE_POSITION       = 69;  // 0x45 - %
const uint8_t AMBIENT_AIR_TEMP                 = 70;  // 0x46 - °C
const uint8_t ABS_THROTTLE_POSITION_B          = 71;  // 0x47 - %
const uint8_t ABS_THROTTLE_POSITION_C          = 72;  // 0x48 - %
const uint8_t ACCELERATOR_PEDAL_POSITION_D     = 73;  // 0x49 - %
const uint8_t ACCELERATOR_PEDAL_POSITION_E     = 74;  // 0x4A - %
const uint8_t ACCELERATOR_PEDAL_POSITION_F     = 75;  // 0x4B - %
const uint8_t COMMANDED_THROTTLE_ACTUATOR      = 76;  // 0x4C - %
const uint8_t TIME_RUN_WITH_MIL_ON             = 77;  // 0x4D - min
const uint8_t TIME_SINCE_CODES_CLEARED         = 78;  // 0x4E - min
const uint8_t MAX_VALUES_EQUIV_V_I_PRESSURE    = 79;  // 0x4F - ratio V mA kPa
const uint8_t MAX_MAF_RATE                     = 80;  // 0x50 - g/s
const uint8_t FUEL_TYPE                        = 81;  // 0x51 - ref table
const uint8_t ETHONOL_FUEL_PERCENT             = 82;  // 0x52 - %
const uint8_t ABS_EVAP_SYS_VAPOR_PRESSURE      = 83;  // 0x53 - kPa
const uint8_t EVAP_SYS_VAPOR_PRESSURE          = 84;  // 0x54 - Pa
const uint8_t SHORT_TERM_SEC_OXY_SENS_TRIM_1_3 = 85;  // 0x55 - %
const uint8_t LONG_TERM_SEC_OXY_SENS_TRIM_1_3  = 86;  // 0x56 - %
const uint8_t SHORT_TERM_SEC_OXY_SENS_TRIM_2_4 = 87;  // 0x57 - %
const uint8_t LONG_TERM_SEC_OXY_SENS_TRIM_2_4  = 88;  // 0x58 - %
const uint8_t FUEL_RAIL_ABS_PRESSURE           = 89;  // 0x59 - kPa
const uint8_t RELATIVE_ACCELERATOR_PEDAL_POS   = 90;  // 0x5A - %
const uint8_t HYBRID_BATTERY_REMAINING_LIFE    = 91;  // 0x5B - %
const uint8_t ENGINE_OIL_TEMP                  = 92;  // 0x5C - °C
const uint8_t FUEL_INJECTION_TIMING            = 93;  // 0x5D - °
const uint8_t ENGINE_FUEL_RATE                 = 94;  // 0x5E - L/h
const uint8_t EMISSION_REQUIREMENTS            = 95;  // 0x5F - bit encoded

const uint8_t SUPPORTED_PIDS_61_80             = 96;  // 0x60 - bit encoded
const uint8_t DEMANDED_ENGINE_PERCENT_TORQUE   = 97;  // 0x61 - %
const uint8_t ACTUAL_ENGINE_TORQUE             = 98;  // 0x62 - %
const uint8_t ENGINE_REFERENCE_TORQUE          = 99;  // 0x63 - Nm
const uint8_t ENGINE_PERCENT_TORQUE_DATA       = 100; // 0x64 - %
const uint8_t AUX_INPUT_OUTPUT_SUPPORTED       = 101; // 0x65 - bit encoded

List of AT Commands:

(https://www.sparkfun.com/datasheets/Widgets/ELM327_AT_Commands.pdf)

const char * const DISP_DEVICE_DESCRIPT       = "AT @1";     // General
const char * const DISP_DEVICE_ID             = "AT @2";     // General
const char * const STORE_DEVICE_ID            = "AT @3 %s";  // General
const char * const REPEAT_LAST_COMMAND        = "AT \r";     // General
const char * const ALLOW_LONG_MESSAGES        = "AT AL";     // General
const char * const AUTOMATIC_RECEIVE          = "AT AR";     // OBD
const char * const ADAPTIVE_TIMING_OFF        = "AT AT0";    // OBD
const char * const ADAPTIVE_TIMING_AUTO_1     = "AT AT1";    // OBD
const char * const ADAPTIVE_TIMING_AUTO_2     = "AT AT2";    // OBD
const char * const DUMP_BUFFER                = "AT BD";     // OBD
const char * const BYPASS_INIT_SEQUENCE       = "AT BI";     // OBD
const char * const TRY_BAUD_DIVISOR           = "AT BRD %s"; // General
const char * const SET_HANDSHAKE_TIMEOUT      = "AT BRT %s"; // General
const char * const CAN_AUTO_FORMAT_OFF        = "AT CAF0";   // CAN
const char * const CAN_AUTO_FORMAT_ON         = "AT CAF1";   // CAN
const char * const CAN_EXTENDED_ADDRESS_OFF   = "AT CEA";    // CAN
const char * const USE_CAN_EXTENDED_ADDRESS   = "AT CEA %s"; // CAN
const char * const SET_ID_FILTER              = "AT CF %s";  // CAN
const char * const CAN_FLOW_CONTROL_OFF       = "AT CFC0";   // CAN
const char * const CAN_FLOW_CONTROL_ON        = "AT CFC1";   // CAN
const char * const SET_ID_MASK                = "AT CM %s";  // CAN
const char * const SET_CAN_PRIORITY           = "AT CP %s";  // CAN
const char * const SHOW_CAN_STATUS            = "AT CS";     // CAN
const char * const CAN_SILENT_MODE_OFF        = "AT CSM0";   // CAN
const char * const CAN_SILENT_MODE_ON         = "AT CSM1";   // CAN
const char * const CALIBRATE_VOLTAGE_CUSTOM   = "AT CV %s";  // Volts
const char * const RESTORE_CV_TO_FACTORY      = "AT CV 0000"; // Volts
const char * const SET_ALL_TO_DEFAULTS        = "AT D";      // General
const char * const DISP_DLC_OFF               = "AT D0";     // CAN
const char * const DISP_DLC_ON                = "AT D1";     // CAN
const char * const MONITOR_FOR_DM1_MESSAGES   = "AT DM1";    // J1939
const char * const DISP_CURRENT_PROTOCOL      = "AT DP";     // OBD
const char * const DISP_CURRENT_PROTOCOL_NUM  = "AT DPN";    // OBD
const char * const ECHO_OFF                   = "AT E0";     // General
const char * const ECHO_ON                    = "AT E1";     // General
const char * const FLOW_CONTROL_SET_DATA_TO   = "AT FC SD %s"; // CAN
const char * const FLOW_CONTROL_SET_HEAD_TO   = "AT FC SH %s"; // CAN
const char * const FLOW_CONTROL_SET_MODE_TO   = "AT FC SM %s"; // CAN
const char * const FORGE_EVENTS               = "AT FE";     // General
const char * const PERFORM_FAST_INIT          = "AT FI";     // ISO
const char * const HEADERS_OFF                = "AT H0";     // OBD
const char * const HEADERS_ON                 = "AT H1";     // OBD
const char * const DISP_ID                    = "AT I";      // General
const char * const SET_ISO_BAUD_10400         = "AT IB 10";  // ISO
const char * const SET_ISO_BAUD_4800          = "AT IB 48";  // ISO
const char * const SET_ISO_BAUD_9600          = "AT IB 96";  // ISO
const char * const IFR_VAL_FROM_HEADER        = "AT IFR H";  // J1850
const char * const IFR_VAL_FROM_SOURCE        = "AT IFR S";  // J1850
const char * const IFRS_OFF                   = "AT IFR0";   // J1850
const char * const IFRS_AUTO                  = "AT IFR1";   // J1850
const char * const IFRS_ON                    = "AT IFR2";   // J1850
const char * const IREAD_IGNMON_INPUT_LEVEL   = "AT IGN";    // Other
const char * const SET_ISO_SLOW_INIT_ADDRESS  = "AT IIA %s"; // ISO
const char * const USE_J1939_ELM_DATA_FORMAT  = "AT JE";     // J1850
const char * const J1939_HEAD_FORMAT_OFF      = "AT JHF0";   // J1850
const char * const J1939_HEAD_FORMAT_ON       = "AT JHF1";   // J1850
const char * const USE_J1939_SAE_DATA_FORMAT  = "AT JS";     // J1850
const char * const SET_J1939_TIMER_X_TO_1X    = "AT JTM1";   // J1850
const char * const SET_J1939_TIMER_X_TO_5X    = "AT JTM5";   // J1850
const char * const DISP_KEY_WORDS             = "AT KW";     // ISO
const char * const KEY_WORD_CHECKING_OFF      = "AT KW0";    // ISO
const char * const KEY_WORD_CHECKING_ON       = "AT KW1";    // ISO
const char * const LINEFEEDS_OFF              = "AT L0";     // General
const char * const LINEFEEDS_ON               = "AT L1";     // General
const char * const LOW_POWER_MODE             = "AT LP";     // General
const char * const MEMORY_OFF                 = "AT M0";     // General
const char * const MEMORY_ON                  = "AT M1";     // General
const char * const MONITOR_ALL                = "AT MA";     // OBD
const char * const MONITOR_FOR_PGN            = "AT MP %s";  // J1939
const char * const MONITOR_FOR_RECEIVER       = "AT MR %s";  // OBD
const char * const MONITOR_FOR_TRANSMITTER    = "AT MT %s";  // OBD
const char * const NORMAL_LENGTH_MESSAGES     = "AT NL";     // OBD
const char * const SET_PROTO_OPTIONS_AND_BAUD = "AT PB %s";  // OBD
const char * const PROTOCOL_CLOSE             = "AT PC";     // OBD
const char * const ALL_PROG_PARAMS_OFF        = "AT PP FF OFF";   // PPs
const char * const ALL_PROG_PARAMS_ON         = "AT PP FF ON";    // PPs
const char * const SET_PROG_PARAM_OFF         = "AT PP %s OFF";   // PPs
const char * const SET_PROG_PARAM_ON          = "AT PP %s ON";    // PPs
const char * const SET_PROG_PARAM_VAL         = "AT PP %s SV %s"; // PPs
const char * const DISP_PP_SUMMARY            = "AT PPS";    // PPs
const char * const RESPONSES_OFF              = "AT R0";     // OBD
const char * const RESPONSES_ON               = "AT R1";     // OBD
const char * const SET_RECEIVE_ADDRESS_TO     = "AT RA %s";  // OBD
const char * const READ_STORED_DATA           = "AT RD";     // General
const char * const SEND_RTR_MESSAGE           = "AT RTR";    // CAN
const char * const READ_VOLTAGE               = "AT RV";     // Volts
const char * const PRINTING_SPACES_OFF        = "AT S0";     // OBD
const char * const PRINTING_SPACES_ON         = "AT S1";     // OBD
const char * const STORE_DATA_BYTE            = "AT SD ";    // General
const char * const SET_HEADER                 = "AT SH %s";  // OBD
const char * const PERFORM_SLOW_INIT          = "AT SI";     // ISO
const char * const SET_PROTOCOL_TO_AUTO_H_SAVE = "AT SP A%c"; // OBD
const char * const SET_PROTOCOL_TO_H_SAVE     = "AT SP %c";  // OBD
const char * const SET_PROTOCOL_TO_AUTO_SAVE  = "AT SP 00";  // OBD
const char * const SET_REC_ADDRESS            = "AT SR %s";  // OBD
const char * const SET_STANDARD_SEARCH_ORDER  = "AT SS";     // OBD
const char * const SET_TIMEOUT_TO_H_X_4MS     = "AT ST %s";  // OBD
const char * const SET_WAKEUP_TO_H_X_20MS     = "AT SW %s";  // ISO
const char * const SET_TESTER_ADDRESS_TO      = "AT TA %s";  // OBD
const char * const TRY_PROT_H_AUTO_SEARCH     = "AT TP A%s"; // OBD
const char * const TRY_PROT_H                 = "AT TP %s";  // OBD
const char * const VARIABLE_DLC_OFF           = "AT V0";     // CAN
const char * const VARIABLE_DLC_ON            = "AT V1";     // CAN
const char * const SET_WAKEUP_MESSAGE         = "AT WM";     // ISO
const char * const WARM_START                 = "AT WS";     // General
const char * const RESET_ALL                  = "AT Z";      // General

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