ELM327LP Datasheet, PDF (38/94 Pages) ELM Electronics – Automatically searches for protocols

ELM327L
Selecting Protocols (continued)
based on any active inputs that are present. If you
need to follow the SAE J1978 order, you should send
the ELM327 an AT SS command first, or step through
each protocol with the TP command.
The automatic search works well with OBDII
systems, but may not be what you need if you are
experimenting. During a search, the ELM327 ignores
any headers that you have previously defined (since
there is always a chance that your headers may not
result in a response), and it uses the default OBD
header values for each protocol. It will also use
standard requests (ie 01 00) during the searches. If
this is not what you want, the results may be a little
frustrating.
To use your own header (and data) values when
attempting to connect to an ECU, do not tell the
ELM327 to use protocol 0. Instead, tell it to either use
only your target protocol (ie. AT SP n), or else tell it to
use yours with automatic searches allowed on failure
(ie AT SP An). Then send your request, with headers
assigned as required. The ELM327 will then attempt to
connect using your headers and your data, and only if
that fails (and you have chosen the protocol with AT
SP An) will it search using the standard OBD default
values.
In general, 99% of all users find that enabling the
memory (setting pin 5 to 5V) and using the ‘Auto’
option when searching (you may need to send AT
SP 0) works very well. After the initial search, the
protocol used by your vehicle becomes the new
default, but it is still able to search for another, without
your having to say AT SP 0 again.
ELM327L DSA
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