A Python emulator of the ELM327 OBD-II adapter connected to a vehicle.

ELM327-emulator provides a virtual serial communication port to client applications (via pseudo-terminal function on UNIX/Linux, or via pyserial library on Windows) and simulates an ELM327 adapter connected to a vehicle through the OBD-II protocol. It includes a command-line interface for extensive monitoring and controlling.

ELM327-emulator is agnostic of the client application accessing the serial port and has been tested with python-OBD.

An internal dictionary (named ObdMessage) allows configuring the emulation, which is currently set to reproduce the message flow generated by a Toyota Auris Hybrid car (through scenario car option), including custom PIDs and can be easily configured to statically and dynamically update its dictionary to simulate OBDII answers produced by other vehicles.

ELM327-emulator supports all protocols allowed by python-OBD; the included dictionary uses the ISO 15765-4 CAN 11 bit ID 500 kbaud protocol.

ELM327-emulator also includes an auxiliary feature (obd_dictionary.py) that builds the PID dictionary of a specific vehicle by automatically querying all standard PIDs one by one (as well as querying additional custom PIDs specified by the user via CSV file). The dictionary can then be used to emulate the specific car.

# Checking Python version (should be 3.5 or higher)
python3 -V

# Installing prerequisites
python3 -m pip install pyyaml
python3 -m pip install pyserial # only needed with Windows
python3 -m pip install tendo # only needed with Windows
python3 -m pip install git+https://github.com/brendan-w/python-OBD.git # this is needed for obd_dictionary.py

# Downloading ELM327-emulator
git clone https://github.com/ircama/ELM327-emulator.git
cd ELM327-emulator

Important note: use an updated version of python-OBD package (e.g., the one installed from GitHub).

The emulator allows batch and interactive mode. The latter is the default and can be executed as follows:

python3 -m elm

After starting the program, the emulator is ready to use. To enable the preconfigured set of PIDs of a Toyota Auris Hybrid car, enter scenario car.

The external application interfacing the emulator just needs to connect to the virtual device shown by the emulator and interact with the vehicle as if it was accessing a real ELM327 adapter.

All subsequent information are not needed for a basic usage of the tool and allow to master ELM327-emulator, exploiting it to test specific features including the simulation of communication exceptions, which are not always easy to be reproduced with a real link.

ELM327-emulator has been tested with Python 3.5, 3.6 and 3.7. Python 2 is not supported.

With UNIX OSs, this code uses pty pseudo-terminals. With Windows, you should first install com0com (a kernel-mode virtual serial port driver), or other virtual serial port software; alterantively, cygwin and Windows Subsystem for Linux (WSL) are supported.

When natively running on Windows, ELM327-emulator requires a virtual serial port driver providing a virtual COM port pair (like com0com), so that one COM port (e.g., COM4) can be used to connect the application and the other one (e.g., COM3) the ELM327-emulator. By default ELM327-emulator uses COM3 serial port; any other port can be set through the -p argument. Example:

python3 -m elm -p COM5

The serial port to be used by the application interfacing the emulator is displayed when starting the program. E.g. on UNIX:

ELM327-emulator is running on /dev/pts/0

When running on Windows, the following message is shown:

ELM327-emulator is running on com0com serial port pair reading from COM3

A dictionary named ObdMessage is used to define commands and PIDs. The dictionary includes more sections (named scenarios):

• 'AT': set of default AT commands
• 'default': set of default PIDs
• 'car': PIDs of a Toyota Auris Hybrid vehicle
• any additional custom section can be used to define specific scenarios

Default settings include both the 'AT' and the 'default' scenarios.

The dictionary used to parse each ELM command is dynamically built as a union of three defined scenarios in the following order: 'default', 'AT', custom scenario (when applied). Each subsequent scenario redefines commands of the previous scenarios. In principle, 'AT' scenario is added to 'default' and, if a custom scenario is used, this is also added on top, and all equal keys are replaced. Then the Priority key defines the precedence to match elements.

If a custom scenario is selected through the scenario command, any key defined in the custom scenario replaces the default settings ('AT' and 'default' scenarios).

The key used in the dictionary consists of a unique identifier for each PID. Allowed values for each key (PID):

• 'Request': received data; a regular expression can be used
• 'Descr': string describing the PID
• 'Exec': command to be executed
• 'Log': logging.debug argument
• 'ResponseFooter': run a function and returns a footer to the response (a lambda function can be used)
• 'ResponseHeader': run a function and returns a header to the response (a lambda function can be used)
• 'Response': returned data; can be a string or a list/tuple of strings; if more strings are included, the emulator randomly select one of them each time
• 'Action': can be set to 'skip' in order to skip the processing of the PID
• 'Header': if set, process the command only if the corresponding header matches
• 'Priority'=number: when set, the key has higher priority than the default (highest number = 1, lowest = 10 = default)

The emulator provides a monitoring front-end, supporting commands and controlling the backend thread which executes the actual process.

At the CMD> prompt, the emulator accepts the following commands:

• help = List available commands (or detailed help with "help cmd").
• quit (or end-of-file/Control-D, or break/Control-C) = quit the program
• counters = print the number of each executed PIDs (upper case names), the values associated to some 'AT' PIDs (cmd_...), the unknown requests, the emulator response delay, the total number of executed commands (commands) and the current scenario (scenario). The related dictionary is emulator.counters.
• pause = pause the execution. (Related attribute is emulator.threadState = THREAD.PAUSED.)
• prompt = toggle prompt off/on if no argument is used, or change the prompt if using an argument
• resume = resume the execution after pausing; also prints the used device. (Related attribute is emulator.threadState = THREAD.ACTIVE)
• delay <n> = delay each emulator response of <n> seconds (floating point number; default is 0.5 seconds)
• wait <n> = delay the execution of the next command of <n> seconds (floating point number; default is 10 seconds)
• engineoff = switch to engineoff scenario
• scenario <scenario> = switch to <scenario> scenario; if the scenario is missing or invalid, defaults to 'car'. The autocompletion (by pressing or double-pressing TAB with Unix systems) allows prompting all compatible scenarios defined in emulator.ObdMessage. (Related attribute is emulator.scenario.)
• default = reset to default scenario
• reset = reset the emulator (counters and variables)
• color = toggle usage of colors off/on
• history [<n>] = print the last 20 items of the command history; if an argument is given, print the last n items in the history; with argument clear, clears the history. The command history is permanently saved to file .ELM327_emulator_history within the home directory.
• merge <module> = import a scenario from an external module and merges it with the emulator configuration. <module> shall be a Python file including the ObdMessage dictionary (e.g., generated by obd_dictionary.py) without .py extension (notice that the physical file shall be in the current directory and shall end with .py). The autocompletion with UNIX systems allows prompting all compatible files in the current directory (type merge, then press space, then press TAB). After a successful merge, the new scenario can be activated through the scenario command.

In addition to the previously listed keywords, any Python command is allowed to query/configure the backend thread.

At the command prompt, cursors and keyboard shortcuts are allowed. Autocompletion (via TAB key) is active with UNIX systems for all previously described commands and also allows Python keywords and namespaces (built-ins, self and global). If the autocompletion matches a single item, this is immediately expanded; Conversely, if more possibilities are matched, none of them is returned, but pressing TAB again a list of available options is displayed. Tab autocompletion is not supported on Windows.

echo and linefeed settings are both disabled by default. They can be configured via related AT commands (ATL1 and ATE1). To enable them via command line:

emulator.counters['cmd_linefeeds'] = True; emulator.counters['cmd_echo'] = True

Space characters are inserted by default in the ECU response as per specification. To remove them, use the AT command ATS0 or emulator.counters['cmd_spaces']=0, Notice that an ATZ command resets all counters.

The emulator includes a timeout management for each entered character, which by default is not active (e.g., set to 1440 seconds). This setting can be configured through emulator.counters['req_timeout']. Decimals are allowed. Some adapters provide a feature that discards characters if each of them is not entered within a short time limit (apart from the first one after a CR/Carriage Return). The appropriate emulation for this timeout is to set emulator.counters['req_timeout']=0.015 (e.g., 15 milliseconds). Typing commands by hand via terminal emulator with such adapters is not possible as the allowed timing is too short. The same happens when setting req_timeout to 0.015.

The command prompt also allows configuring the emulator.answer dictionary, which has the goal to dynamically redefine answers for specific PIDs ('Pid': '...'). Its syntax is:

emulator.answer = { 'pid' : 'answer', 'pid' : 'answer', ... }

Example:

emulator.answer = { 'SPEED': 'NO DATA\r', 'RPM': 'NO DATA\r' }
# Or, alternatively:
emulator.answer['SPEED']='NO DATA\r'
emulator.answer['RPM']='NO DATA\r'

The above example forces SPEED and RPM PIDs to always return "NO DATA".

To reset the emulator.answer string to its default value:

emulator.answer = {}
# Or, alternatively:
del emulator.answer['SPEED']
del emulator.answer['RPM']

To simulate that the adapter is not connected to the vehicle:

emulator.answer['AT_R_VOLT'] = '0.0V'

This dictionary can be used to modify answers within a workflow. The front-end allows implementing basic Python workflows and, when used in batch mode, can also be controlled by a piped external supervisor. The following examples show some simple workflows in interactive mode.

Example of automation which suspends the emulator for 10 seconds:

emulator.threadState = THREAD.PAUSED; time.sleep(10); emulator.threadState = THREAD.ACTIVE

Example of an automation that simulates the off/on ignition states:

CMD> for i in range(10): emulator.scenario="car" if i % 2 else "engineoff"; print(emulator.scenario); time.sleep(10)
engineoff
car
engineoff
car
engineoff
car
engineoff
car
engineoff
car

Response strings allow embedding Python statements and expressions. Specifically, Response, ResponseHeader, ResponseFooter and emulator.answer support single and multiple in-line Python commands (expressions or statements) when embraced between \0 tags: this feature for instance can be used to embed real-time delays between strings or to differentiate answers. The return value of a statement is ignored. The evaluation of an expression is substituted. Spaces inside \0 tags are allowed and can be used to improve readability. Example: 'Response' = 'SEARCHING...\0 time.sleep(1) \0\rUNABLE TO CONNECT\r'. This returns SEARCHING..., then waits one second, then returns \rUNABLE TO CONNECT\r. Notice that, as time.sleep is a statement, the related return value is ignored.

Further processing can be achieved through a lambda function applied to ResponseHeader, ResponseFooter. It has to manage the following parameters: self, cmd, pid, val (e.g., lambda self, cmd, pid, val:).

• cmd: the request, received by the client application
• pid: the PID identifier (which can be used as key to index self.counters and ObdMessage)
• val: ObdMessage value related to pid (e.g., val['Response']).

Example of PID definition within the ObdMessage dictionary:

            'ELM_PIDS_A': {
                'Request': '^0100$',
                'Descr': 'PIDS_A',
                'ResponseHeader': \
                lambda self, cmd, pid, val: \
                    'SEARCHING...\0 time.sleep(1) \0\rUNABLE TO CONNECT\r' \
                    if self.counters[pid] == 1 else 'NO DATA\r',
                'Response': '',
                'Priority': 5
            },

In the above example, the first time ResponseHeader is executed, the produced response is SEARCHING..., followed by a one-second delay and then \rUNABLE TO CONNECT\r. For all subsequent messages, the response will be different and produces 'NO DATA\r'.

The ability to add dynamic differentiators and delays within responses enables testing specific use cases and exceptions that are difficult to be achieved through a real connection with a car. These not only apply to the ObdMessage dictionary (by editing obd_message.py), but also to emulator.answer, that can be configured through the command line. Consider for instance the following dynamic configuration via command line:

emulator.answer['SPEED'] = '\0 ECU_R_ADDR_E + " 03 41 0D 0A " if randint(0, 100) > 20 else "NO DATA" \0\r'

In the above example, which illustrates an in-line expression substitution, the configuration of the ‘SPEED’ PID (Vehicle speed is replaced with a dynamic answer and the ‘SPEED’ PID will return 7E8 03 41 0D 0A + newline for most of the times. With 20% probability, NO DATA + newline is returned. Notice that the last \r is common to both options.

The following example shows how to dynamically generate an answer via command line by converting decimal numbers to hex string in order to allow confortable testing of a PID by specifying decimal input values. Suppose that the PID needs to double the input. We use CUSTOM_FUEL_LEVEL PID in the example, testing the answer related to 15.5 liters.

Preliminarily, test number conversion with the command line:

"%.2X" % int(15.5*2)
1F

Apply it to CUSTOM_FUEL_LEVEL PID so that it returns 7C0 03 61 29 1F \r':

emulator.answer['CUSTOM_FUEL_LEVEL'] = '7C0 03 61 29 \0 "%.2X" % int(15.5*2) \0 \r'

Or, alternatively, use the header variable instead of the header digits:

emulator.answer['CUSTOM_FUEL_LEVEL'] = '\0 ECU_R_ADDR_I + " 03 61 29 " + "%.2X" % int(15.5*2) \0 \r'

The following command sets SPEED (Vehicle speed to 60 km/h via command line (60 can be changed to any integer value between 0 and 255):

emulator.answer['SPEED'] = '\0 ECU_R_ADDR_E + " 03 41 0D %.2X" % 60 \0\r'

The following command sets RPM (Engine RPM to 500 via command line:

emulator.answer['RPM'] = '\0 ECU_R_ADDR_E + " 04 41 0C %.4X" % int(4 * 500) \0\r'

To list the configuration, type emulator.answer, or simply counters. To remove the dynamic answer and return to the default configuration of the ‘SPEED’ PID, type del emulator.answer['SPEED'].

Command to configure PID '0100' answer (PIDS_A) to BUS INIT: OK for its first query and to 48 6B 13 41 00 BE 1F B8 11 AD \r for all the subsequent queries:

emulator.answer['ELM_PIDS_A'] = '\0 "BUS INIT: OK" if self.counters["ELM_PIDS_A"] < 2 else "48 6B 13 41 00 BE 1F B8 11 AD \\r" \0'

The ELM_PIDS_A counter (emulator.counters["ELM_PIDS_A"]) can be reset with:

emulator.counters["ELM_PIDS_A"] = 0

Logs are written to elm.log, file, rotated to elm.log.1 and elm.log.2 when its size reaches 1 MB. Logging is controlled through the elm.yaml file (in the current directory by default). Its path can be set through the ELM_LOG_CFG environment variable. This file follows the Python’s builtin logging module format and allows customizing the configuration of the logging process.

The logging level can be dynamically changed through logging.getLogger().handlers[n].setLevel(). To check that console is the first handler (e.g., handlers[0]), run for n, l in enumerate(logging.getLogger().handlers): print(n, l.name). For instance, if console refers to the first handler (default settings of the provided elm.yaml file), the following commands will change the logging level:

logging.getLogger().handlers[0].setLevel(logging.DEBUG)
logging.getLogger().handlers[0].setLevel(logging.INFO)
logging.getLogger().handlers[0].setLevel(logging.WARNING)
logging.getLogger().handlers[0].setLevel(logging.ERROR)
logging.getLogger().handlers[0].setLevel(logging.CRITICAL)

It is possible to add marks in the log file via commands like logging.info("my mark")

To totally disable logging for all handlers: logging.disable(logging.CRITICAL). To restore logging: logging.disable(0).

Command to count the number of different PIDs (OBD Commands) used by the client (excluding AT Commands):

import re
from functools import reduce
reduce(lambda x, key: x + (1 if re.match('^[A-Z]', key) and not key.startswith('AT_') and emulator.counters[key] > 0 else 0), emulator.counters, 0)

The following command returns the total number of OBD Commands (PID queries issued by the client excluding AT Commands):

import re
from functools import reduce
reduce(lambda x, key: x + (emulator.counters[key] if re.match('^[A-Z]', key) and not key.startswith('AT_') else 0), emulator.counters, 0)

To only count AT Commands:

from functools import reduce
reduce(lambda x, key: x + (emulator.counters[key] if key.startswith('AT_') else 0), emulator.counters, 0)

Print the average number of processed commands per second within a 5 seconds period:

a=emulator.counters['commands'];time.sleep(5);print((emulator.counters['commands']-a)/5)

To save a CSV file including the emulator.counters dictionary:

with open('mycounters.csv', 'w') as f: f.write('\r\n'.join([x + ', ' + repr(emulator.counters[x]) for x in emulator.counters]))

obd_dictionary is a dictionary generator for "ELM327-emulator".

It queries the vehicle via python-OBD for all available commands and is also able to process custom PIDs described in Torque CSV files.

Its output is a Python ObdMessage dictionary that can either replace the obd_message.py module of ELM327-emulator, or extend the existing dictionary via merge command, so that the emulator will be able to provide the same commands returned by the vehicle.

Notice that querying the vehicle might be invasive and some commands can change the car configuration (enabling or disabling belts alarm, enabling or disabling reverse beeps, clearing diagnostic codes, controlling fans, etc.). In order to prevent dangerous PIDs to be used for building the dictionary, a PID blacklist (blacklisted_pids) can be edited in elm.py. To check all PIDs without performing actual OBDII queries (dry-run mode), use the -p 0 option (the standard error output with default logging level shows the list of produced PIDs).

usage: obd_dictionary.py [-h] -i DEVICE [-c CSV_FILE] [-o FILE] [-v] [-V]
                         [-p PROBES] [-d DELAY] [-D DELAY_COMMANDS]
                         [-n CAR_NAME] [-b] [-t [FILE]] [-m]

optional arguments:
  -h, --help            show this help message and exit
  -i DEVICE             serial port connected to the ELM327 adapter (required
                        argument)
  -c CSV_FILE, --csv CSV_FILE
                        input csv file including custom PIDs (Torque CSV
                        Format: https://torque-bhp.com/wiki/PIDs) '-' reads
                        data from the standard input
  -o FILE, --out FILE
                        output dictionary file generated after processing
                        input data (replaced if existing). Default is to print
                        data to the standard output
  -v, --verbosity       print process information
  -V, --verbosity_debug
                        print debug information
  -p PROBES, --probes PROBES
                        number of probes (each probe includes querying all
                        PIDs to the OBDII adapter)
  -d DELAY, --delay DELAY
                        delay (in seconds) between probes
  -D DELAY_COMMANDS, --delay_commands DELAY_COMMANDS
                        delay (in seconds) between each PID query within all
                        probes
  -n CAR_NAME, --name CAR_NAME
                        name of the car (dictionary label; default is "car")
  -b, --blacklist       include blacklisted PIDs within probes
  -x, --noautopid       do not autopopulate the pid list with the set of
                        built-in commands supported by the vehicle; only use
                        csv file.
  -t [FILE], --at [FILE]
                        include AT Commands within probes. If a dictionary
                        file is given, also extract AT Commnands from the
                        input file and add them to the output
  -m, --missing         add in-line comment to dictionary for PIDs with
                        missing response

Sample usage: obd_dictionary.py -i /dev/ttyUSB0 -c car.csv -o ObdMessage.py -v -p 10 -d 1 -n mycar

obd_dictionary.py exploits the command discovery feature of python-OBD which autopopulates the set of builtin commands supported by the vehicle through queries performed within the connection phase. Optionally, this set can be further enriched with a list of custom PIDs included in an input csv file in Torque CSV Format. The autopopulation feature can be disabled with -x option.

In general, ELM327-emulator should already manage all needed AT Commands within its default dictionary, so in most cases it is worthwhile removing them from the new scenario via -t option.

The file produced by obd_dictionary.py provides the same information model of obd_message.py. It can be used to replace the default module or can be dynamically imported in ELM327-emulator through the merge command, which loads an ObdMessage dictionary and merges it to emulator.ObdMessage. Example of merge process:

# Create AurisOutput.py
python3 obd_dictionary.py -i /dev/ttyUSB0 -c auris.csv -o AurisOutput.py -n Auris
python3 -m elm # run ELM327-emulator
merge AurisOutput
scenario Auris

To help configuring the emulator, autocompletion is allowed (by pressing TAB) with UNIX systems when prompting the merge command, including the merge argument. Also variables and keywords like scenario accept autocompletion, including the scenario argument.

A merged scenario can be removed via del emulator.ObdMessage['<name of the scenario to be removed>'].

To produce a complete dictionary file that can replace obd_dictionary.py:

python3 obd_dictionary.py -i /dev/ttyUSB0 -c auris.csv -o obd_dictionary.py -n default -t elm/obd_message.py

ELM327-emulator can be run in batch mode to allow automating tests and background execution. The -b FILE option allows this mode and writes the output to FILE. The first line in that file will be the virtual serial device, which can be read to a shell variable through read variable_name < output_file. Commands can be piped in (e.g., within a bash script) to configure the emulator (e.g., via echo -e). The appropriate way to kill a background instance of the emulator is with the SIGINT signal (kill -2). To ensure that the external application is started only after correct setup of the emulator, the input commands can be terminated with a string (e.g., "RUNNING") that can then be recognised before starting the application.

The description of the ELM327-emulator command-line option is the following:

Usage: python3 -m elm [-h] [-b FILE]

optional arguments:
  -h, --help            show this help message and exit
  -b FILE, --batch FILE
                        Run ELM327-emulator in batch mode. Argument is the
                        output file. The first line in that file will be the
                        virtual serial device

 - ELM327 OBDII adapter emulator

The following script shows an example of batch mode usage. obd_dictionary.py is run after starting ELM327-emulator in background and is used here as example of external application interfacing the emulator. The output of the emulator is saved to $FILE and the background process id is saved to $EMUL_PID.

FILE=/tmp/elm$$
echo -e 'scenario car\ncounters\n"RUNNING"' | python3 -m elm -b $FILE &
EMUL_PID=$!

until grep "^RUNNING$" $FILE; do sleep 0.5; done
read TTYNAME < $FILE

../obd_dictionary.py -i /dev/pts/0 -o $TTYNAME -t -v -o /dev/null

kill -SIGINT $EMUL_PID
cat $FILE
rm $FILE

Many thanks to @qqj1228 for implemeting support to com0com Windows driver as well as for other enhancements.