Opening /dev/cu.usbserial-A50285BI @ 10400 baud (settle 2.0s)...
-> b'ATZ\r'
<- 4 bytes:
   hex   : 41 54 5a 0d
   ascii : 'ATZ\r'

Exact echo of what was sent -- for a raw K-Line (KKL/FTDI) adapter this IS the expected good result: it means the wire, transceiver, and pinout are electrically sound (K-Line is half-duplex -- your own bytes always come back). It does NOT mean the ECU answered anything; only a real KWP2000 exchange (tunie info --adapter kline) exercises that.

(full session log: logs/tunie-raw-20260826-214846.txt)