sterretje:
As far as I understand it, OP does not send anything. Just receives from a device.
well yes that was my initial understanding but I had a look at the code he attached and it states
// Work in progress
// [color=red]Give this a J1587 series of values in monitor[/color] and it will search for and return rpm. load and turbo values to monitor
// Try to resolve issue of a data byte having the same value as a PID byte we are looking for
// Modified structure to create a function
and further in the code he mentions
while (Serial.available() > 0) // Using test input data: 80 5A 66 BE E0 2E 5C 55 BE E0 2E
suggesting that the User is entering that data possibly manually in the console
Hence my comment.