K-Line vs. L-Line Bus Protocols: Differences and Similarities

This page compares K-line and L-line protocols, highlighting their similarities and differences, including signal and interface details.

Introduction

K-line and L-line are communication protocols employed within the automotive industry for tasks like diagnostics and control.

The K-line protocol is defined in ISO-9141 and operates as a single-wire serial communication protocol. It facilitates bidirectional communication between a diagnostic tool and various Electronic Control Units (ECUs) within the vehicle. The ISO-9141 standard outlines electrical characteristics, signal encoding, timing, and frame structure.

The L-line protocol is also a single-wire communication protocol used in the automotive domain. Its specifications are detailed in ISO 9141-2 or ISO 14230-2.

Similarities Between K-line and L-line Protocols

The following points summarize the similarities between K-line and L-line protocols:

• Both K-line and L-line support similar data rates, typically around 10.4 kbps (Kilobits per second).
• Both K-line and L-line use similar signal voltage levels: Logic-1 (0V to 4V) and Logic-0 (7V to 12V).
• Both support half-duplex communication.

Note: Signal voltage levels and data rates can vary depending on specific implementations, ECU specifications, and vehicle manufacturers.

Differences Between K-line and L-line Protocols

The following points summarize the difference between K-line and L-line protocols.

• K-line is utilized as a communication medium through the OBD-II (On-Board Diagnostics II) port, whereas the L-line signal is used for bus initialization.
• K-line is interfaced to pin number 7 of the OBD-II port, while L-line is interfaced to pin number 15.
• L-line is often used in conjunction with K-line to provide extended diagnostic capabilities.