connector or cable wiring scheme
9 pin D-SUB female connector at the computer
16 pin car OBD2 special connector at the car (looking into the car-side connector)
This adapter wires the OBD-II 16-pin Data Link Connector (DLC) to a 9-pin D-SUB serial (RS-232) port on a PC for use with vehicles that implement the ISO 9141-2 or ISO 14230-4 KWP2000 diagnostic protocol over the K-line on pin 7 of the DLC. Both protocols share the same K-line physical layer: 10.4 kbaud, 8N1, half-duplex, idle high at 12 V via a pull-up resistor. ISO 9141-2 uses 5-baud slow initialisation whilst KWP2000 additionally supports fast initialisation. These protocols were common on Chrysler, European, and Asian vehicles from roughly 2000 to 2007, prior to the mandatory adoption of CAN (ISO 15765-4) for US market vehicles from 2008.
Scheme 1
Scheme 2
Used for Volkswagen, Audi, Skoda, Seat.
Notes
- The OBD-II DLC is defined by SAE J1962 / ISO 15031-3 as a 16-pin trapezoidal female connector, Type A (12 V systems) or Type B (24 V, distinguished by an interrupted centre groove).
- Mandatory DLC pins on all OBD-II variants: pin 4 (chassis ground), pin 5 (signal ground), and pin 16 (battery positive, 12 V for Type A).
- Pin 7 carries the K-line; pin 15 carries the optional L-line, used only during the wake-up/initialisation phase and in the tester-to-ECU direction only.
- ISO 9141-2 slow init: the tester sends the target address byte at 5 bps (200 ms per bit); the ECU replies with sync byte 0x55, then keyword bytes KW1 and KW2; the tester acknowledges with the complement of KW2; the ECU echoes the complement of the address; normal communication then proceeds at 10.4 kbaud.
- KWP2000 fast init: K-line is pulled low for 25 ms then released high for 25 ms, after which standard 10.4 kbaud communication begins immediately.
- Maximum message length: 260 bytes. Data format: 1 start bit, 8 data bits, no parity, 1 stop bit (8N1).
- The RS-232 signal conditioning in this adapter is a third-party interface circuit; the RS-232 conversion is not specified by ISO 9141-2 or ISO 14230-4.