ELM327 — connection

The ELM327 transport connects an adapter through a Windows serial COM port. Install the ELM327 package in Settings → Packages. If the adapter needs a driver to expose its port, install that driver separately.

Usage limitations

ELM327 is recommended for low-traffic sessions. Do not use it for ECU firmware updates. Frames may be lost on a busy bus; choose another CAN adapter when you need a complete capture.

Connection steps

1. Connect the adapter to the computer and make sure Windows has assigned a COM port to it. Close other applications using that port.
2. Select the required profile and module, such as Automotive → VAG.
3. With the connection closed, open Settings → Connections → Transport and select Type → ELM327.
4. Select the adapter's Port and wait for the check to finish. Firmware version and Device description show information read from the selected device. Use Rescan to repeat discovery and compatibility checks.
5. If the required features are supported, set CAN bitrate to 250000 or 500000 to match the bus.
6. Connect and open Tracer or Monitor.

The serial port speed is detected automatically; no manual selection is needed. CAN identifiers with 11 and 29 bits are received together, with no separate format selector. This transport uses a COM port; it does not provide IP address or Wi-Fi connection settings.

Compatibility check

A version label such as ELM327 v1.5 does not establish compatibility. Devices reporting the same version can support different commands. Use the check result and the displayed limitations:

• If required commands are unsupported, connection is blocked and the CAN bitrate setting is disabled. You can select another port or adapter.
• For a partial limitation, read the warning before connecting: it explains which mode is unavailable or needs additional configuration.
• If the adapter has not been checked or its information is outdated, close the connection and use Rescan.

Classical CAN is supported. CAN FD, RTR frames, and sending frames without data are unavailable. Some adapters can only send frames containing eight data bytes; this limitation is shown in settings.

CAN acknowledgements during monitoring

On a separate bench, an ECU may need another CAN node to acknowledge received frames. If a warning reports missing acknowledgements, use another active node on the bus or the adapter configuration offered in the warning.

For a suitable ELM327, the warning includes Try enabling CAN acknowledgements permanently via PP21?. Close the connection, follow the link, and review the Enable CAN acknowledgements dialog. Apply saves the setting in the adapter's memory and restarts it; the setting persists after power off. Cancel leaves it unchanged. Normal checks and connections do not change this persistent setting.

The dialog also offers the maximum verified serial baud rate, up to 500000 baud. Select this option to save the higher speed with the acknowledgement setting.

After Apply, a short progress log replaces the warning. It disappears automatically on success. If the operation fails, the log remains visible; use Rescan before retrying and the cross in the top-right corner to dismiss the log.

Serial baud rate, below Port, shows the working speed of the serial port while connected and the last detected speed when disconnected. It is independent of CAN bitrate and is read-only.

When a non-default serial baud rate is detected, the Restore defaults icon to the right returns the adapter to 38400 baud and disables PP21 after confirmation. Progress is shown in the same place.

If the saved speed cannot be confirmed after restart, the log shows the expected and detected speeds. Use Restore defaults to clear the saved setting, or run Rescan before retrying.

If connection fails

• No ELM327 in Type: check the installed package and selected module.
• No port: check the connection and Windows driver, then use Rescan.
• The port is listed but the check fails: close other applications using it and read the compatibility warnings. A different ELM327 version label does not guarantee a solution.
• Connected but no frames: check the CAN bitrate, wiring, and whether traffic is present. On a separate bench, also check CAN acknowledgements.

See connection troubleshooting for further checks.