Automotive test automation using the ELM327 OBD module

On-board diagnostics (OBD) conforming to the OBD-II standard are available on all modern cars manufactured for sale in the US, EU, Japan and Australia.

The ELM327 module from ELM Electronics provides a convenient interface to the OBD protocols.

To find out whether a particular vehicle supports OBD-II, check the manufacturer's documentation and/or the sites in the External Resources section at the bottom of this page.

ELM327 OBD Perl module

This module provides a Perl interface to a device containing an Elm Electronics ELM327 OBD Interpreter and provides access to the following functions:

Read OBD parameters and extract individual values from results
Read OBD Trouble Codes and expand them to their full form
Reset OBD Trouble Codes
Read ELM327 parameters
Write and write the ELM327 data byte
Calibrate ELM327 Voltage
Switchable diagnostic trace and replay function for debugging

The module is written entirely in Perl and works with both Linux and Windows. Depending on which operating system it is run on it uses either the Win32::SerialPort or Device::SerialPort module so it should work on any platform that supports one of them.

It currently supports most of the ISO standard commands and has been tested on a couple of European CAN-based vehicles (Ford and GM). I would be very interested to see debug info produced by other vehicles: particularly non-CAN models.

I currently have very little information about manufacturer specific commands and would be grateful for any information that googling doesn't turn up. There's a small amount of data on various Fords, but very little on GM models.

My next challenge will be to get the module working on android using Scripting Layer for Android (SL4A). I'm currently getting errors while trying to set up a bluetooth connection so it doesn't look quite as easy as I'd hoped.

It can be downloaded from CPAN.

Application Examples

Show some OBD parameters and any Trouble codes:

Read and display some OBD parameters and any Trouble codes and monitor some more OBD parameters, reading values once every second:

#!/usr/bin/perl

use strict;
use warnings;

use Device::ELM327;

my $debug_level = 0; # 0 to suppress debug output, >0 to print it

my $port_name=undef;

if ($^O eq "MSWin32")
{
  $port_name='COM5';
}
else
{
  $port_name='/dev/ttyUSB0';
}

my $obd = Device::ELM327->new($port_name, $debug_level);

#*****************************************************************

# Read status information...

my $id=$obd->GetELM();
print "Interface type: $id\n";

my $ign=$obd->GetIgnition();
print "Ignition: $ign\n";

$obd->ShowTroubleCodes();

my @values_to_read_at_start =
(
  "Vehicle Identification Number",
  "Calibration Identifications",
  "Calibration Verification Numbers",
  "Monitor status since DTCs cleared",
  "OBD requirements to which vehicle is designed",
  "In-use Performance Tracking",
  "Auxiliary Input Status",
);

my @values_to_monitor =
(
  "Time Since Engine Start",
  "Input Voltage",
  "Control Module Voltage",
  "Ambiant Air Temperature",
  "Intake Air Temperature",
  "Engine Coolant Temperature",
  "Catalyst Temperature Bank 1, Sensor 1",
  "Catalyst Temperature Bank 1, Sensor 2",
  "Catalyst Temperature Bank 2, Sensor 1",
  "Catalyst Temperature Bank 2, Sensor 2",
  "Absolute Throttle Position",
  "Engine RPM",
  "Vehicle Speed Sensor",
  "Commanded Secondary Air Status",
  "Air Flow Rate from Mass Air Flow Sensor",
  "Monitor status this driving cycle",
  "Intake Manifold Absolute Pressure",
  "Fuel Rail Pressure relative to manifold vacuum",
  "Fuel Rail Pressure (gauge)",
  "Fuel Rail Pressure",
  "Intake Manifold Absolute Pressure",
  "Ignition Timing Advance for #1 Cylinder",
);

DisplayValues($obd, \@values_to_read_at_start);

# Read these values once a second...
do
{
  DisplayValues($obd, \@values_to_monitor);
  sleep 1;
    
} while (0);

#*****************************************************************

undef $obd;

#*****************************************************************

sub DisplayValues
{
  my ($obd, $array_reference) = @_;

foreach my $value (@$array_reference)
  {
    my $response = $obd->Read($value);

if ($response->{'status'} eq "ok")
    {
      foreach my $result (@{$response->{'results'}})
      {
        print "$result->{'address'} - $result->{'name'}: $result->{'value'} $result->{'unit'}\n"
      }
    }
    else
    {
      print "Error $response->{'status'} while trying to read $value\n";
    }
    print "\n";
  }
}

Greencroft Technical Services

Automotive test automation using the ELM327 OBD module

ELM327 OBD Perl module

Application Examples

Show some OBD parameters and any Trouble codes:

Read and display some OBD parameters and any Trouble codes and monitor some more OBD parameters, reading values once every second:

Display every value that the module can read from the ECU:

Replay previously captured OBD commands and responses:

External resources

OBD trouble code definitions

OBD commands