BMW fitted a proprietary 20-pin round connector in the engine bay of its vehicles from approximately 1988 to 2000, covering models such as the E30, E34, E36, E38, E39, E46, and Z3. The connector carries BMW’s DS2 (Diagnostic System 2) protocol, a proprietary diagnostic bus that runs over the K-line physical layer at 9600 baud with 8-bit data, no parity, and one stop bit (8N1). DS2 is not standardised by SAE or ISO; BMW never published a public connector or protocol specification. From model year 2000 onward, BMW vehicles also carry the standard 16-pin OBD-II Data Link Connector in the passenger compartment as required by regulation.
20 pin car OBD2 special connector at the car side
| Pin | Signal | Description |
|---|---|---|
| 14 | Battery power | |
| 15 | ISO 9141-2 L Line | |
| 17 | ISO 9141-2 K Line | |
| 19 | GND | |
| 20 | ISO 9141-2 K Line |
Notes
The connector is located in the engine bay, not the passenger compartment. It is a round 20-pin proprietary housing; only a subset of pins are documented. The DS2 protocol uses half-duplex K-line signalling: idle state is 12 V (line pulled high), and the transmit-low state is 0 V. Pin 17 and pin 20 both carry the ISO 9141-2 K-line signal; their individual roles within the DS2 framing are not publicly documented. Pin 15 carries the L-line, used as an optional unidirectional wake-up line during initialisation. Functions of the remaining pins are unknown.
Signals
- Battery power — unswitched battery positive supply to the diagnostic interface (pin 14)
- ISO 9141-2 L Line — optional unidirectional wake-up line used during bus initialisation (pin 15)
- ISO 9141-2 K Line — bidirectional half-duplex diagnostic data line; DS2 protocol runs at 9600 baud, 8N1 (pins 17 and 20)
- GND — ground reference for the diagnostic bus (pin 19)
References
- ISO 9141-2:1994 — Road vehicles — Diagnostic systems — Part 2: CARB requirements for interchange of digital information — governs the K-line / L-line physical layer used by this connector
- ISO 9141-2 and K-Line: 5-Baud Handshake Guide — K-line electrical characteristics and initialisation procedures
- Automotive Diagnostic Standards — overview of ISO and SAE diagnostic standard families