Having a discussion on smog checkpoints over at Calguns.net in the off topic room. Poached this comment:
"Wtf you talking about?
I work at a smog shop. OBDII is plugged in for a rpm tach signal, also reads the ECU, checks for monitor ready status.
We have 2 ESP smogs machines. 1 old, and one brand new, newest version. Same as what the CHP uses. There is no way to read if you've had a reflash from the machine. Dealerships can access it and see that it's been flashed, but not a smog machine. No way it can read if the fuel tables have been adjusted ect."