Recomended circuits are in SAE J2201 and ISO-9141-2 publications. Consists of a comparator and a transistor. I can supply a kit for $22 Will post a schematic in near future. Alex C. Peper OBD-2 developer http://www.obd-2.com > Does anyone know where I can find a diy circuit to connect an OBDII ISO-9141 to the serial port of a PC ?. > > TIA > Wayne. >