looking at ODB2

K-Line (ISO 9141) is a communication protocol primarily used in automotive diagnostics, allowing a scan tool or ECU to communicate with a vehicle’s onboard systems. It’s commonly found in OBD-II systems, particularly in older European and Asian vehicles.

Key Features of K-Line (ISO 9141)

1. Single-Wire Communication – Uses a single K-Line for data transmission.
2. Asynchronous Serial Communication – Typically operates at 10.4 kbps.
3. Half-Duplex Communication – Can send and receive data but not at the same time.
4. Voltage Levels:
   • High (Mark) = 12V (Idle state)
   • Low (Space) = 0V (Active state)
5. Handshake & Initialization:
   • Requires a “5-baud” wake-up signal to initiate communication.
   • Switches to 10.4 kbps after initialization.

ISO 9141 vs. Other Protocols

• ISO 9141-2: A refined version used in OBD-II, adding error checking.
• KWP2000 (ISO 14230): Successor to ISO 9141 with faster speeds and additional features.
• CAN Bus (ISO 11898): Replaced K-Line in most modern vehicles due to higher speed and robustness.

Hardware & Interface

• K-Line (Pin 7 on OBD-II connector): Main communication line.
• L-Line (Pin 15, optional): Used for wake-up in some implementations.
• Common Interfaces:
  • ELM327-based tools (USB, Bluetooth, or WiFi) support ISO 9141.
  • FTDI chips (FT232RL) for direct UART communication with K-Line.

Applications

• Reading and clearing DTCs (Diagnostic Trouble Codes).
• Accessing ECU parameters (RPM, temperature, fuel trim).
• Flashing ECUs in some older vehicles.

Breaking it down to practical use

In practical applications, NMEA 2000 is often seen in combination with J1939 or ISOBUS. For example, some boat engines use J1939 internally and deploy a gateway/filter to parse certain information onto standardized NMEA 2000 PGNs. In some cases, NMEA 2000 and J1939 messages even co-exist on the same CAN bus. This is possible as none of the NMEA 2000 PGNs overlap with J1939 PGNs. Similarly, NMEA 2000 messages are often broadcast onto an ISOBUS network since many GPS modules are used in both maritime and agricultural use cases. See our ISOBUS intro for details.

Where is this going and where am I heading?

I have this diesel truck that is ODB1. It’s proprietary. Because this truck is pre electronic madness it will run post apocalyptic and i want to keep it that way.
Right now it has many analog gauges but I want to add a second instrument panel, a fully electronic OBD2. This will require many decisions to begin with so it’s not included in this post

The Nema2000 specification will probably do the trick, it’s finding sensors and a database that can all jive. There are a few configured automotive digital displays but they are over 1000 dollars to get started so I will have to build this out on my own