Use Fitlet as an Automotive Diagnostic Analyzer and Monitor

Application notes using fitlet. Credit goes to user Hassellbear for publishing more than enough cool application notes to justify a dedicated sub-forum.

Moderator: hassellbear

Post Reply
Posts: 106
Joined: Mon May 28, 2012 12:25 pm

Use Fitlet as an Automotive Diagnostic Analyzer and Monitor

Post by hassellbear »


The world's automotive fleet is now almost universally equipped with On-Board Diagnostic (OBD) systems. These OBD systems in conjunction with external reader/programmers allow users to monitor numerous real-time system parameters, read diagnostic trouble codes for use in repairs, and reset trouble codes.

Using relatively inexpensive hardware and software, Fitlet can function as a very capable OBD Analyzer and Monitor. Some possible applications for Fitlet in this role are:

1. Diagnostic station at automotive repair facility.

2. "Carputer" providing vehicle performance data in addition to other functions such as navigation and mobile media center.

3. Performance tuning aid for the speed lovers among us.
Uses.jpeg (221.64 KiB) Viewed 11172 times

Some OBD Specifics


OBD systems have evolved over time and exhibit some differences based on region. A partial list of the variations includes:

ALDL: (Assembly Line Diagnostic Link): An early General Motors Implementation

OBD-I: An early regulatory mandated implementation which lacked standardization between manufacturers resulting in manufacturer specific diagnostic link connectors, diagnostic trouble codes, and methods for reading codes. Diagnostic codes were often presented by blinking the "Check Engine" light using code specific patterns.

OBD-1.5: A partial implementation of the present day OBD-II standard which was primarily used by General Motors.

OBD-II: The dominant present day standard which offers improved standardization of diagnostic connector type, data protocols, and diagnostic trouble codes.

EOBD: The European equivalent of OBD-II which uses the same connector type and data protocols as OBD-II

JOBD: A variant of OBD-II for the Japanese market

ADR 79/01 & 79/02: Austrailian implementations of OBD-II

This App-Note focuses on OBD-II since it is the basis for most of the currently deployed systems.

OBD-II Data Protocols

There are five allowable protocols for OBD-II compliant systems. They are:

1. J1850 PWM (Pulse Width Modulation)
2. J1850 VPW (Variable Pulse Width)
3. ISO9141-2 (Asynchronous Serial)
4. ISO14230-4/KWP2000 (Keyword Protocol 2000)
5. ISO15765-4/SAE J2480 (Variant of CAN)

A partial list of protocols by vehicle manufacturer and model year can be found here: ... tocols.pdf

OBD-II Diagnostic Connectors

The form and pinouts of connectors used in OBD-II systems are specified by SAE Standard J1962. These connector types which are shown in the following images have 2 forms which are Type A and Type B.

Connector Types
J1962Connectors.jpg (56.33 KiB) Viewed 11180 times

Connector Pinout
obdiipinout.jpg (56.65 KiB) Viewed 11174 times

Posts: 106
Joined: Mon May 28, 2012 12:25 pm

Use Fitlet as an Automotive Diagnostic Analyzer and Monitor

Post by hassellbear »


The hardware used in this demonstration is:

1. Fitlet iA10
2. ELM 327 Based OBD-II Interface - Bluetooth Version - Compatible With All OBD-II Protocols
Hardware.jpeg (80.95 KiB) Viewed 11172 times
For information about the ELM 327 interface see:

As is often the case, clones of Elm's products are available. I am using a clone which has consistently performed well.


Normally I prefer open source software for such projects, but in this case the pyobd package I tried did not adequately support computer - vehicle communications via bluetooth.Pyobd expects to connect to serial ports designated as tty... instead of as rfcomm0. Standard port redirection/reassignment techniques were unable to overcome this problem. Perhaps a future version of Pyobd will support bluetooth.

Fortunately, a reasonably priced payed alternative called OBD Auto Doctor is available for Linux. It is very capable and does a good job of supporting bluetooth communications. It offers a wealth of features include real-time graphical and tabular presentation of parameters that are too numerous to list. See:

Software Installation

OBD Auto Doctor is available in .deb and in tar archive format. Unfortunately, the AMD64 .deb offered is corrupted and will not install. However, installation using the tar archive works well. To download the software navigate to

Installation of the archive version consists of extracting its contents into a directory of your choice and copying the file obdautodoctor.desktop into the folder /usr/share/applications so that OBD Auto Doctor will appear in the Linux Mint Menu.

In order for Linux Mint to recognize the file obdautodoctor.desktop you must edit it to point to the program's location. The original and unedited files are shown below.

Original obdautodoctor.desktop

[Desktop Entry]
Name=OBD Auto Doctor
Comment=OBD Car Diagnostics Software

Edited obdautodoctor.desktop

[Desktop Entry]
Name=OBD Auto Doctor
Comment=OBD Car Diagnostics Software

Use the following website to guide you in the editing process needed for Linux Mint.

Interfacing Fitlet To The Vehicle

1. Locate the test vehicles OBD-II connector and plug in the ELM 327 Adapter. Typically that connector is located at the bottom of the dash on the driver's side.

2. Launch OBD Auto Doctor initiate the bluetooth link. This should be a seamless process.


The results of this test were quite good. Fitlet was able to communicate with my vehicle via bluetooth out to a range of around 40 feet/12 meters. The selection of systems data available for monitoring was comprehensive and extensive.
Screenshots1.jpg (245.47 KiB) Viewed 11172 times
Screenshots2.jpg (245.81 KiB) Viewed 11172 times


1. Fitlet can be a cost effective viable option for vehicle systems analysis and monitoring in the home or professional repair shop setting. By using the bluetooth connectivity option, one Fitlet station could easily handle multiple vehicles by using multiple ELM 327 Bluetooth adapters. However, because the Fitlet - Elm 327 Interface - OBD Auto Doctor solution is relatively inexpensive, it shouldn't represent an excessive cost burden to outfit each repair bay with its own Fitlet system.

2. For those considering using Fitlet as a "Carputer", OBD-II monitoring could be a useful function.

3. Fitlet is undoubtedly very versatile.

Post Reply

Return to “Cool stuff with fitlet”