PROTOCOL · PHYSICAL LAYER · 1996-2010
K-Line protocol
K-Line (ISO 9141-2 / ISO 14230 Layer 1).
What is K-Line?
K-Line is the single-wire bidirectional physical-layer protocol that carried diagnostic communication on European vehicles from 1996 to roughly 2010. Speed is typically 10.4 kbit/s. Bidirectional half-duplex — the tester and ECU take turns talking on the same wire. Carried KWP2000 (ISO 14230) or KW1281 (VAG proprietary) application layer.
Key characteristics
- Single wire — usually OBD pin 7 on the J1962 connector.
- Speed: 10.4 kbit/s (very slow vs modern CAN at 500 kbit/s).
- Init: 5-baud (slow, deprecated) or fast init.
- Used by Bosch EDC15 / EDC16 / ME7 / Motronic ME7.5 / Siemens SIMOS 2/3.
- Cheap clone flashers (MPPS V13, KKL cable, Galletto) work on K-Line.
- Mostly obsolete on EU diesels since ~2010 (replaced by CAN-OBD).
K-Line service IDs / frame structure
| ID / Code | Name | Purpose |
|---|---|---|
5-baud init | Slow start | Legacy init — sends address at 5 baud |
Fast init | Bit-banged wake-up | Faster init for KWP2000 |
10.4 kbit/s | Operational speed | Diagnostic data rate |
Half-duplex | Bidirectional | Tester and ECU share the wire |