diff --git a/README.md b/README.md
index 32bff39..348e9c5 100644
--- a/README.md
+++ b/README.md
@@ -127,6 +127,7 @@ The emulator provides a monitoring front-end, supporting commands and controllin
 At the `CMD> ` prompt, the emulator accepts the following commands:
 
 - `help` = List available commands (or detailed help with "help cmd").
+- `loglevel` = If an argument is given, set the logging level, otherwise show the current one. Valid numbers: CRITICAL=50, ERROR=40, WARNING=30, INFO=20, DEBUG=10.
 - `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 = emulator.THREAD.PAUSED`.)
@@ -190,7 +191,13 @@ 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.
+The `emulator.ELM_R_UNKNOWN` parameter allows customizing the message returned in case of unknown/invalid command. The default message is `?\r`, with an addition of a trailing `\r`. This message can be customized; for example, to just get `\r`, set the following:
+
+```python
+emulator.ELM_R_UNKNOWN = ''
+```
+
+The 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:
 
@@ -216,7 +223,7 @@ car
 
 ## Configuring response strings
 
-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.
+Response strings allow embedding Python statements and expressions. Specifically, `Response`, `ResponseHeader`, `ResponseFooter`, `emulator.answer` and `emulator.ELM_R_UNKNOWN` 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:`).
 
@@ -241,7 +248,7 @@ Example of PID definition within the `ObdMessage` dictionary:
 
 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:
+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` and `emulator.ELM_R_UNKNOWN`, that can be configured through the command line. Consider for instance the following dynamic configuration via command line:
 
 ```python
 emulator.answer['SPEED'] = '\0 ECU_R_ADDR_E + " 03 41 0D 0A " if randint(0, 100) > 20 else "NO DATA" \0\r'
@@ -300,7 +307,21 @@ 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](https://docs.python.org/3/howto/logging.html) 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](https://docs.djangoproject.com/en/2.2/topics/logging/#a-quick-logging-primer) 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:
+The logging level can be dynamically changed through the `loglevel` command.
+
+To read the current log level:
+
+```shell
+loglevel
+```
+
+To set log level to debug:
+
+```shell
+loglevel 10
+```
+
+Alternatively, the logging level can be set 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:
 
 ```python
 logging.getLogger().handlers[0].setLevel(logging.DEBUG)
diff --git a/elm/__version__.py b/elm/__version__.py
index 3f6fab6..8a81504 100644
--- a/elm/__version__.py
+++ b/elm/__version__.py
@@ -1 +1 @@
-__version__ = '1.0.3'
+__version__ = '1.0.4'
diff --git a/elm/elm.py b/elm/elm.py
index fb978af..cb97ff5 100644
--- a/elm/elm.py
+++ b/elm/elm.py
@@ -24,7 +24,7 @@
 import traceback
 import errno
 from random import randint
-from .obd_message import ObdMessage, ECU_ADDR_E, ELM_R_OK
+from .obd_message import ObdMessage, ECU_ADDR_E, ELM_R_OK, ELM_R_UNKNOWN
 from .__version__ import __version__
 
 
@@ -103,6 +103,7 @@ def setSortedOBDMsg(self):
 
     def __init__(self, batch_mode=False, serial_port=""):
         self.ObdMessage = ObdMessage
+        self.ELM_R_UNKNOWN = ELM_R_UNKNOWN
         self.set_defaults()
         self.setSortedOBDMsg()
         self.batch_mode = batch_mode
@@ -323,9 +324,9 @@ def write(self, resp):
                     except Exception as e:
                         logging.error("Cannot execute '%s': %s", i, e)
             else:
-                logging.debug("Write: %s", repr(i))
                 if nospaces:
                     i = re.sub(r'[ \t]+', '', i)
+                logging.debug("Write: %s", repr(i))
                 if os.name == 'nt':
                     self.master_fd.write(i.encode())
                 else:
@@ -425,7 +426,7 @@ def handle(self, cmd):
                     logging.error(
                         "Internal error - Missing response for %s, PID %s",
                         cmd, pid)
-                    return self.ELM_R_OK
+                    return ELM_R_OK
         if "unknown_" + cmd not in self.counters:
             self.counters["unknown_" + cmd] = 0
         self.counters["unknown_" + cmd] += 1
@@ -437,7 +438,7 @@ def handle(self, cmd):
                          repr(cmd), self.counters["cmd_header"])
         else:
             logging.info("Unknown ELM command: %s", repr(cmd))
-        return ""
+        return self.ELM_R_UNKNOWN
 
     def sanitize(self, cmd):
         cmd = cmd.replace(" ", "")
diff --git a/elm/interpreter.py b/elm/interpreter.py
index e8e7e87..74b2bae 100644
--- a/elm/interpreter.py
+++ b/elm/interpreter.py
@@ -190,6 +190,19 @@ def do_reset(self, arg):
         self.emulator.set_defaults()
         print("Reset done.")
 
+    def do_loglevel(self, arg):
+        "If an argument is given, set the logging level,\n"\
+        "otherwise show the current one.\n"\
+        "CRITICAL=50, ERROR=40, WARNING=30, INFO=20, DEBUG=10."
+        if arg and arg.isnumeric():
+            logging.getLogger().handlers[0].setLevel(int(arg))
+            print("Logging level set to",
+                logging.getLogger().handlers[0].level)
+        else:
+            print(
+                "Current logging level:",
+                    logging.getLogger().handlers[0].level)
+
     def do_counters(self, arg):
         "Print the number of each executed PID (upper case names), the values\n"\
         "associated to some 'AT' PIDs, the unknown requests, the emulator response\n"\
diff --git a/elm/obd_message.py b/elm/obd_message.py
index 55bae86..6d2c16c 100644
--- a/elm/obd_message.py
+++ b/elm/obd_message.py
@@ -15,6 +15,7 @@
 ECU_R_ADDR_S = "7B8"  # Responses sent by 7B0 Skid Control ECU 7B0/7B8
 
 ELM_R_OK = "OK\r"
+ELM_R_UNKNOWN = "?\r"
 ELM_MAX_RESP = '[0123456]?$'
 
 # This dictionary uses the ISO 15765-4 CAN 11 bit ID 500 kbaud protocol
diff --git a/obd_dictionary/__init__.py b/obd_dictionary/__init__.py
index 8498854..59afc46 100644
--- a/obd_dictionary/__init__.py
+++ b/obd_dictionary/__init__.py
@@ -20,7 +20,7 @@
 ecu = {
     "7B0": 'ECU_ADDR_S',   # Skid Control address ECU
     "7B8": 'ECU_R_ADDR_S', # Responses sent by 7B0 Skid Control ECU 7B0/7B8
-    "7E2": 'ECU_ADDR_H',   # HVECU address (Hybrid contol module)
+    "7E2": 'ECU_ADDR_H',   # HVECU address (Hybrid control module)
     "7EA": 'ECU_R_ADDR_H', # Resp. sent by HVECU (Hybrid Ctrl module) 7E2/7EA
     "7E0": 'ECU_ADDR_E',   # Engine ECU address
     "7E8": 'ECU_R_ADDR_E', # Responses sent by ECM (engine Ctrl module) 7E0/7E8
@@ -181,7 +181,7 @@ def obd_dictionary():
         type=argparse.FileType('r'),
         nargs="?",
         help='include AT Commands within probes. '
-             'If a dictionary file is given, also extract AT Commnands'
+             'If a dictionary file is given, also extract AT Commands'
              ' from the input file and add them to the output',
         metavar='FILE')
     parser.add_argument(
@@ -296,7 +296,9 @@ def obd_dictionary():
 
     # Print header information
     print("\n".join([ecu[k] + ' = "' + k + '"' for k in ecu]))
-    print('ELM_R_OK = "OK\\r"\nELM_MAX_RESP = "[0123456]?$"\n')
+    print('ELM_R_OK = "OK\\r"\n'
+          'ELM_R_UNKNOWN = "?\r"\n'
+          'ELM_MAX_RESP = "[0123456]?$"\n')
     print("ObdMessage = {")
     print("    '" + args.car_name + "': {")