OBD-II Protocol

OBD systems give the vehicle owner or repair technician access to the status of the various vehicle subsystems

Hands-on guide to on-board diagnostic app development

What vehicles OBD-II covers?

CarVan

Truck

B2B and B2C applications

FLEET MANAGEMENT PERSONAL USE

Cloud

OBD-II Reader

Smart Adapter

OBD-II Reader

Cigarette Socket

B2B and B2C applications

INSURANCE CAR MAINTENANCE

Cloud

OBD-II Reader

Operator

Cloud

OBD-II Reader

Operator

Wiki

Tasks

EML 327

The ELM327 is a programmed microcontroller produced by ELM Electronics for translating

the on-board diagnostics (OBD) interface found in most modern cars. A bridge between the

onboard computer in a car and handheld device

● Scan OBD-II system for codes

● Read PIDs

● Clear codes

● Aid in diagnostics

Types of adapters

USB

Bluetooth

WiFi

● Most widely compatible option

● Relatively inexpensive due to no wireless radio

● No chance of a dropped connection

● The cable can get in the way

● Relatively inexpensive

● Bluetooth is available in a lot of devices

● Incompatible with some devices, like iPhones

● Compatible with more devices than Bluetooth

● Expensive

● Provide troubleshooting information or tips

● Record and playback live data

● Graph data or graph specific PIDs

● Read manufacturer or pending codes

● Utilize functions that require bi-directional communication

Tools

Scan ToolsCode Reader● Read and display codes

● Clear codes

● Reset the check engine light

Mobile platforms. Android & iOS

Primary devices that can work with ELM327

SmartphonesTablets

Laptops

Exception is iPhone, iPod Touch and iPad

due to how Apple handles Bluetooth stack.

Apple MFi Program

Emulator & car

Emulator Car

Step 1

Connect the OBDII to your vehicle’s/emulator’s OBDII port and

start/run the car/emulator

Step 2

Go to Settings on your Android phone

Step 3

Choose one type of connections WiFi or Bluetooth

according to used adapter

WiFi/Bluetooth connection

WiFi/Bluetooth connection

Step 4

Check that the Bluetooth/WiFi is turned on and tap on the OBDII

device from list

Step 5

Enter 1234 when prompted

Step 6

Launch your favorite app

Type of widgets

Gauge style

Numeric style

Plot Style

4 Param Style

Check engine

● Occasional flashes show momentary malfunctions

● It stays on if the problem is of a more serious nature, affecting the emissions output or safety of the vehicle.

● A constantly flashing MIL is a sign of a major problem which can cause serious damage if the engine is not stopped immediately.

Wiki

What is freeze frame?

Freeze Frame is an element of the Diagnostic Executive that stores engine operating conditions

at the moment an emission-related fault is stored in memory (when the MIL is commanded on).

This data can be used to help identify the cause of an emissions-related fault

Data Recorded

● DTC Description

● Engine Speed

● Vehicle Speed

● Airflow

● Engine Load

● Fuel Pressure

● Fuel Trim Value

● Engine Coolant Temperature

● Intake Manifold Pressure

● Open or Closed Loop Status

Obd2 modes

● to identify what powertrain information is available to the scan tool

● displays Freeze Frame data

● lists the emission-related "confirmed" diagnostic trouble codes stored

● used to clear emission-related diagnostic information

● displays the oxygen sensor monitor screen and the test results gathered about the oxygen

sensor

● a request for on-board monitoring test results for continuously and non-continuously monitored

system

● a request for emission-related diagnostic trouble codes detected during current or last

completed driving cycle

● could enable the off-board test device to control the operation of an on-board system, test, or

component

● used to retrieve vehicle information (VIN, CALID, CVN etc)

● lists emission-related "permanent" diagnostic trouble codes stored

Read RPM or speed

Get vehicle RPM/SPEED Send PID

Mobile App

OBD-II LibraryELM 327

Wireless Adapter ECU

Send PID

Deliver response Return response in hex format

Convert tohuman-readable format

Protocol

OBD-II library

Adapter Model

Connector

Command Executor

Service

Describes the protocol to use

(Wi-Fi or Bluetooth)

● uses socket opened by Connector

● schedules commands in a serial manner

● notifies execution status

Object describing OBD-II adapter (MAC

address, name, Protocol)

● enable Bluetooth or Wi-Fi

● connects and disconnects from adapter

● opens socket

● tracks connection state and notifies the system

● uses Connector to track state

● delivers commands from user to

executor and back

● notifies about connection and

execution state

<>

● Phone and adapter are paired only once

● And the next time phone will immediately connect with

adapter

How to identify that adapter is plugged into a different car?

Car 1VIN 1

Car 2VIN 2

Car 3VIN 3

Adapter

Send Mode 09 PID 02

Receive 0140:4902013147311:4A4335343434522:37323532333637

Extract VIN "1G1JC5444R7252367"

Thank you!

If you have a project idea in mind, but don`t know where

to start, we're here to help you with literally everything

from discovery, proof of concept development, project

scoping to design and estimate.

We would be happy to help you with our expertise.info@lemberg.co.uk

Links

List of sources used for our demo:● http://www.obdii.com/background.html

● https://en.wikipedia.org/wiki/On-board_diagnostics

● https://en.wikipedia.org/wiki/ELM327

● http://cartech.about.com/od/Glossary/a/The-Elm327-Programmed-Microcontroller.htm

● http://www.auto-facts.org/resetcheckenginelight.html

● http://www.autozone.com/repairguides/S-T-Series-Blazer-Bravada-Envoy-Jimmy-Rainier-Trailblazer-Xtreme/OBD-System-Terminology/Freeze-Frame-Data/_/P-0996b43f80cb37ca