Opensource LS Flashing(It's Closer Than You Think)

[kur4o]

Currently the hardware is pretty simple. It's 4 resistors, 1 diode and 1 optocoupler. All the magic is done in the Arduino code.

I was almost sure you had used some cheap vpw transiever like motorola 33990 or similar auto grade one.
It is waste of time and effort to turn the arduino in software transiever when you can hook a simple piece of hardware to do it. Not sure how stable will be in car and off the bench test. Noise might be a big stability problem if software can`t compensate. Anyway big respect for the effort. I just want to express that it might not be the most economical approach.
VPW is 0-7 volt signal, so I guess the needed hardware is to change the 0-5 volts on the Arduino tx-rx line.
If you want to go cheaper and software only, ditch the Arduino and link the motorola transiever with 2$ usb to ttl and find a way to control the 4x switch.

The ELm is interesting and not the buffer but the main obstacle is that you cannot send hex data over it. You have to convert from ascii characters, and what a nightmare is to change the header.