ELM322
Resetting Trouble Codes
The ELM322 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:
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, though, that the ELM322 does not monitor the
content of 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 (the ignition on but
the engine not running, etc.) before they will respond
to a mode 04 command.
- 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 ELM322, as it occurs whenever a scan tool is used
to reset your codes. Understand that the loss of this
data could cause your car to run poorly for a short time
while the system recalibrates itself.
That is all there is to clearing the codes. Once
again, be very careful not to inadvertently issue an 04!
To avoid inadvertently erasing stored information,
Error Messages
When problems occur, the ELM322 will respond
with one of the following short messages. Here is a
brief description of each…
DATA ERROR
The ELM322 expects at least four bytes for every
message, and less than that were received. This
may have been caused by the key being turned off,
or a loose connection, for example, or by receiving a
single byte header message when a three byte
header was expected. Any monitoring that was in
progress will have been aborted. Try turning the
display of headers on to see what was actually sent.
BUS BUSY
The ELM322 tried to send the mode command or
request for about 0.5 seconds without success.
Messages are all assigned priorities, which allows
one message to take precedence over another.
More important things may have been going on, so
try re-issuing your request.
NO DATA
There was no response from the vehicle before a
timeout occurred. The mode requested may not be
supported, so the vehicle ignored you, or the timeout
value was set too short, or possibly the ignition key
was not turned to the ‘on’ position. Try issuing an 01
00 command to be sure that the vehicle is ready to
receive commands, and if that works, try adjusting
the timeout to a longer value with the Set Timeout
AT command.
BUS ERROR
An attempt was made to send a message, and the
data bus voltage did not change as expected. This is
most likely because of a circuit problem (a short or
open), so check all of your wiring carefully.
<DATA ERROR
There was a problem with the data checksum (CRC
byte), indicating a data error in the line pointed to
(the ELM322 still shows you what it received). There
could have been a circuit problem, or a noise burst
which interfered, so try re-sending the request again.
?
This is the standard response for a misunderstood
command received on the RS232 bus. Usually it is
due to a typing mistake.
ELM322DSE
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