From this thread
Each ECU can now have a different response speed, measured in ms. For example:
That creates five ECUs, with delays varying from 1ms up to 1 second.
obdsim -g Random -d 7 -g Random -d 3 -g Random -d 1000 -g Random -d 1 -g Cycle -d 6
If you connect to that, the default timeout is such that the third ECU will time out and you won't see a response. Set it to be very high using ATSTFF and you'll see the last ECU takes a noticable amount of time to reply, but will eventually appear just before getting the ">" prompt.