ELM327LSM datasheet(59/94 Pages) ELM

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ELM327L DSA

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ELM327L

02: 00 00 01 5F 05 02 31

03: 6D 05 03 03 FF FF FF

if the headers are off. Note that multiframe messages

always send eight bytes of data, and fill in unused byte

positions with FFs.

With the headers off, a multiline response looks

very similar to the multiline responses for ISO15765-4.

The first line shows the total number of bytes in the

message, and the other lines show the segment

number, then a colon, and the data bytes received.

Note that the byte count is a hexadecimal value (ie the

‘012’ shown means that there are 18 bytes of data).

The single line that shows 012 in the above (the

total number of data bytes) is actually a special type of

response, called a ‘Connection Management’ or

‘TP.CM’ message. It has a specific format, but the only

bytes that are typically relevant are those that provide

the total message size in bytes, so that is all that the

ELM327 normally shows. In order to see the other

bytes, you must turn CAN Auto Formatting off (AT

CAF0), and then repeat the request. Note that this will

only show the entire TP.CM message if you have a

version 1.4b or newer ELM327.

This has been a brief description of how to use

the ELM327 in a typical J1939 environment. If you can

monitor for information, make global requests as well

as specific ones, and receive single or multiframe

responses, then you have the tools necessary to

diagnose most vehicle problems.

Using J1939 (continued)

Several European heavy duty truck and bus

manufacturers have joined to form an organization for

standardizing the way in which information is retrieved

from these large vehicles. The result of their work is

the FMS (or Fleet Management Systems) Standard,

and the Bus-FMS Standard.

The FMS standard is based on a subset of the

250 kbps J1939 protocol, which uses only broadcast

messages

for

the

information.

order

not

compromise the integrity of the vehicle’s CAN bus, the

standard also specifies a gateway device to provide

separation between (potentially unskilled) users and

the critical control information on the vehicle.

The information contained in the FMS messages

is defined by PGNs, using the same PGN numbers as

for J1939. The difference is that they only define a

small subset of those specified by J1939.

To monitor the information provided by an FMS

gateway, simply use the AT MP command with the

appropriate PGN number. We should caution that

some information (VIN, software version, etc.) is only

transmitted every 10 seconds, so some patience is

required when waiting for the data.

The FMS Standard

The FMS standard is completely open, and still

evolving (as of this writing, the most recent update was

version 2.00). For more information, visit the FMS web

sites:

FMS Standard

www.fms-standard.com

Bus FMS Standard

bus-fms-standard.com

ELM327LSM Datasheet(PDF) 59 Page - ELM Electronics

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