Cars · Wiring
OBD1 CN2 Serial Port Reference
Technical reference for the OBD1 ECU CN2 serial port, detailing its pinout and role in datalogging.
The CN2 header is the dedicated 5-pin serial communication port found on OBD1 Honda ECUs. It serves as the primary interface for ECU-to-PC communication, essential for real-time datalogging and ROM programming.
Pinout Mapping
| Pin | Function | Description |
|---|---|---|
| 1 | GND | Ground |
| 2 | RX | Receive (from PC) |
| 3 | +5V | Logic Power |
| 4 | TX | Transmit (to PC) |
| 5 | N.C. | Not Connected |
Operational Notes
- Half-Duplex: In stock form, the CN2 port operates in half-duplex mode (RX and TX are shared/connected).
- Full-Duplex Modification: Removing the J12 jumper on the ECU board separates the receive and transmit lines, enabling full-duplex communication. This is recommended for more reliable high-speed datalogging.
- Hardware Interface: The ECU communicates at TTL (5V logic) voltage levels. An appropriate RS232-to-TTL signal translator is required to interface with standard PC serial or USB ports.
Always verify your board layout and silkscreen labels if available, as variations can occasionally occur between different ECU part numbers.