Specifications

Error Messages
Resetting Trouble Codes
When hardware or data problems are
encountered, the ELM323 will respond with one of the
following short messages. Here is a brief description of
each:
BUS BUSY
The ELM323 tried to send the mode command or
initialize the bus, but detected too much activity to
insert a message. This could be because the bus was
in fact busy, but is often due to wiring problems that
result in a continuously active input at OBDIn.
FB ERROR
This message is sent when a ‘feedback’ error is
detected. When the K Line is first energized, a check
is made to ensure that the signal is seen at OBDIn. If it
does not appear there, this message is displayed.
Check your wiring before proceeding.
DATA ERROR
There was a response from the vehicle, but the
information was incorrect or could not be recovered. In
the case of a bus initialization, this error signifies that
the format bytes received were not as required, so
initiation could not continue. If the error occurs during
normal operation, it means that the response did not
contain enough bytes to be a valid message (which
can occur if the signal is interrupted during a data
transmission).
<DATA ERROR
The error checksum result was not as expected,
indicating a data error in the line pointed to (the
ELM323 still shows you what it received). There could
have been a noise burst which interfered, or a circuit
problem. Try re-sending the command.
NO DATA
The IC waited for the period of time that was set
by AT ST, and detected no response from the vehicle.
It may be that the vehicle had no data to offer, that the
mode requested was not supported, or that the vehicle
was attending to higher priority issues and could not
respond to the request in the allotted time. Try
adjusting the AT ST time to be sure that you have
allowed sufficient time to obtain a response.
?
This is the standard response for a misunderstood
command received on the RS232 bus. Usually it is due
to a typing mistake.
The ELM323 is quite capable of resetting
diagnostic trouble codes, as this only requires issuing
a mode 04 command. The consequences should
always be considered before sending it, however, as
more than the MIL (or ‘Check Engine’ lamp) will be
reset. In fact, issuing a mode 04 will:
- reset the number of trouble codes
- erase any diagnostic trouble codes
- erase any stored freeze frame data
- erase the DTC that initiated the freeze frame
- erase all oxygen sensor test data
- erase mode 06 and 07 test results
Clearing of all of this information is not unique to
the ELM323 – it occurs whenever a scan tool is used
to reset the codes. The biggest problem with losing
this data is that your vehicle may run poorly for a short
time, while it performs a recalibration.
To avoid inadvertently erasing stored information,
the SAE specifies that scan tools must verify that a
mode 04 is intended (“Are you sure?”) before actually
sending it to the vehicle, as all trouble code
information is immediately lost when the mode is sent.
Recall that the ELM323 does not monitor the content
of the messages, so it will not know to ask for
confirmation of the mode request – this would have to
be the duty of a software interface if one is written.
As stated, to actually erase diagnostic trouble
codes, one need only issue a mode 04 command. A
response of 44 from the vehicle indicates that the
mode request has been carried out, the information
erased, and the MIL turned off. Some vehicles may
require a special condition to occur (eg. the ignition on
but the engine not running) before they will respond to
a mode 04 command.
That is all there is to clearing the codes. Once
again, be very careful not to accidentally send an 04!
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ELM323