Standard CAN (ISO 15765-4) OBD requires that all messages have 8 data bytes - (ELM327 documentation)
Reading from my car with a bluetooth ELM327 I get messages that are not all 8 bytes long.
Here is the configuration :
AT Z # Reset
AT D # Default
AT SP 6 # Set Protocol
AT CFC1 # Flowcontrol
AT D1 # Show DLC
AT AL # Allow long messages
AT H1 # Show headers
AT CAF0 # Disable Formatting
AT L0 # Disable linefeeds
AT S0 # Remove whitespace
The output :
Command: AT MA
17A8FFFFFFAA00F031A3
17E8FFFFFF00FF4000FF
186719503203200020
0C6880637FFF800E8E82
2BC8948641FD03891D73
18A6FFF000064000
1F68DE20003700FFFFFF
1F88F504826FFE000A0D
391600008000C000
12E8C77FFF7FE0FFFF00
24270200FFEFFE000C
29C800000000FFFF0000
35245C000000
130800286FFE009FFECD
17A8FFFFFFAA00F031A3
17E8F
BUFFER FULL
Here most messages are correct (3 bytes ID + 1 byte DLC + 8 bytes Data), but some are shorter and sometimes I recieve messages that are longer. Are these normal ? If not, any ideas where it could come from ?
It is true that all OBD related (i.e. standardized) messages have 8 bytes of data. However the trace you have posted does not contain any OBD messages.
OBD messages have a CAN-ID between 0x7DF and 0x7EF
The messages in your output seem to be other (manufacture-specific) CAN messages. The manufacture is free to define the format of those messages, thus a DLC of less than 8 is allowed.