OBDHow to Guide

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What is OBD?

OBD is an acronym for “on-board diagnostics” and refers to vehicle's self-diagnostics and reporting capability.

Originally it was intended to help mechanics run quick vehicle diagnostics.

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OBD Chip

First of all, you would need a OBDII adapter to be able to use the OBDII interface. There are many adapters from different manufacturers. Some of them have a COM interface, others have a USB interface, and some have a Bluetooth interface

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How it works

Theoretically, any adapter can be used by the Android application, but in practice, your best choice is the Bluetooth interface.

Also, adapters can be differentiated by supported OBDII protocols (i.e. by supported vehicles).

So if you have a car within reach and good OBDII adapter we can start developing OBDII reader application.

You can use OBD Simulator software also.

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OBD Simulator

The one that worked for me is OBDSim: it is an open source project available for different platforms.

A hardware emulator can be used instead of a real car. I used ECUsim 2000 standard with ISO 15765 (CAN) protocol enabled.

As for the OBDII adapter - I used ELM327 v.1.5 adapter.

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Developing the application

Let's start with describing the protocol that is used for communication between Android device and OBDII adapter/vehicle.

It is text-based polling type protocol. This means that all you need is to send a command to receive a response. And knowing what commands to send is key.

We will connect to the adapter through Bluetooth. It seems that Bluetooth Low Energy API is just the thing we should use.

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The protocol supports AT commands like turning echo and control line feed. Another part of the protocol is OBDII control protocol itself.

The general workflow of the application functionality should go like this:

1) connect to the OBDII adapter through Bluetooth;

2) initialize OBDII adapter with AT commands;

3) continuously get data from the vehicle through issuing the corresponding PID codes.

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Connecting to the OBDII adapter is straightforward. But one thing you need to do before connecting is to select the Bluetooth device. Displaying an alert dialConnecting to the OBDII adapter is straightforward. But one thing you need to do before connecting is to select the

Bluetooth device. Displaying an alert dialogue with single choice items is a good way to go:ogue with single choice items is a good way to go:

Connection with OBD Adapter

Connecting to the OBDII adapter is straightforward.

But one thing you need to do before connecting is to select the Bluetooth device. Displaying an alert dialogue with single choice items is a good way to go.

The UUID I mentioned represents a “serial” interface through Bluetooth. Of course, this code should be executed in a non-UI thread.

Also, I would recommend checking this article for details and a solution of a bug in Android that can lead to connection failure in some cases.

Don't forget to initialize the OBDII adapter first by issuing configuration commands

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new EchoOffObdCommand().run(socket.getInputStream(), socket.getOutputStream());new LineFeedOffObdCommand().run(socket.getInputStream(), socket.getOutputStream());new TimeoutObdCommand().run(socket.getInputStream(), socket.getOutputStream());new SelectProtocolObdCommand(ObdProtocols.AUTO).run(socket.getInputStream(), socket.getOutputStream());

OBD Configuration Commands

new EchoOffObdCommand().run(socket.getInputStream(), socket.getOutputStream());

new LineFeedOffObdCommand().run(socket.getInputStream(), socket.getOutputStream());

new TimeoutObdCommand().run(socket.getInputStream(), socket.getOutputStream());

new SelectProtocolObdCommand(ObdProtocols.AUTO).run(socket.getInputStream(), socket.getOutputStream());

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Measuring RPM & Speed

EngineRPMObdCommand engineRpmCommand = new EngineRPMObdCommand();

SpeedObdCommand speedCommand = new SpeedObdCommand();

while (!Thread.currentThread().isInterrupted())

{

engineRpmCommand.run(sock.getInputStream(), sock.getOutputStream());

speedCommand.run(sock.getInputStream(), sock.getOutputStream());

// TODO handle commands result

Log.d(TAG, "RPM: " + engineRpmCommand.getFormattedResult());

Log.d(TAG, "Speed: " + speedCommand.getFormattedResult());

}

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OBD II Trouble Codes

OBD-II codes consist of a number of parts. Here is a sample OBD2 code:

P0171

The first character identifies identifies the system related to the trouble code. P = Powertrain B = Body C = Chassis U = Undefined

The second digit identifies whether the code is a generic code (same on all OBD-II equpped vehicles), or a manufacturer specific code. 0 = Generic (this is the digit zero -- not the letter "O") 1 = Enhanced (manufacturer specific)

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new EchoOffObdCommand().run(socket.getInputStream(), socket.getOutputStream());new LineFeedOffObdCommand().run(socket.getInputStream(), socket.getOutputStream());new TimeoutObdCommand().run(socket.getInputStream(), socket.getOutputStream());new SelectProtocolObdCommand(ObdProtocols.AUTO).run(socket.getInputStream(), socket.getOutputStream());

The third digit denotes the type of sub-system that pertains to the code

1 = Emission Management (Fuel or Air) 2 = Injector Circuit (Fuel or Air) 3 = Ignition or Misfire 4 = Emission Control 5 = Vehicle Speed & Idle Control 6 = Computer & Output Circuit 7 = Transmission 8 = Transmission 9 = SAE Reserved 0 = SAE Reserved

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new EchoOffObdCommand().run(socket.getInputStream(), socket.getOutputStream());new LineFeedOffObdCommand().run(socket.getInputStream(), socket.getOutputStream());new TimeoutObdCommand().run(socket.getInputStream(), socket.getOutputStream());new SelectProtocolObdCommand(ObdProtocols.AUTO).run(socket.getInputStream(), socket.getOutputStream());

OBD Code Explained

The most common OBD-II codes are P0xxx powertrain codes, along with P2xxx generic & P3xxx generic codes (please scroll down).

For the other OBD-II codes, choose from Bxxxx - B Codes - OBD-II Body Codes or Cxxxx - C Codes - Chassis Codes, and Uxxxx - U - Network Codes.

If your DTC (diagnostic trouble code) begins with P1xxx, that means it's a manufacturer specific code

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Let's Analyse OBD Codes

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Know Car's Health Now

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