My question concerns 0x7E8 response messages where the message is greater than 8 bytes.
I am sure OBD2 experts won't need much of the detail below but for the sake of clarity......
When a diagnostic device (eg scantool) sends a 0x7DF message with a Mode and PID value, most 0x7E8 responses consist of a single message of up to 8 bytes.
However some response messages require more than 8 bytes. eg request for the VIN and many vehicle manufacturer specific Mode/PID values. In this case ISO 15765-2 specifies that the first response 0x7E8 message has the code 0x10, Number of bytes, Mode, PID followed by data.
The diagnostic device then responds with a 0x7E0 flow control message according to the ISO 15765-2 spec. Noting that there is no information in that flow control message to identify which 0x7E8 response message is being flow controlled.
When the flow control message is received, the responding device then sends further 0x7E8 messages with the 0x2? code where "?" is the sequence number of the message. Again there is no information is those further 0x7E8 messages to identify which 0x7DF message Mode/PID is being responded to.
So my question is - Is it possible to have 2 or more diagnostic devices on an OBD2 bus sending 0x7DF messages where the response is more than 8 bytes?
As there is no information in either the 0x7E0 flow control message or the following 0x7E8 0x2? coded messages to identify the original 0x7DF request, multiple diagnostic devices on the OBD2 bus will not be able to identify which 0x7E8 response messages correspond to their request.
I have seen this 0x7E8 message confusion happen in practice with more than one scantool connected to a vehicle. But maybe I have missed something?
