Connection & Adapters

The ObdConnection class is the main entry point for communicating with a vehicle. It handles adapter detection, initialization, command execution, and ELM327 response parsing.

Creating a Connection

Auto-Detection (recommended)

When no adapter profile is specified, Connect sends an ATI command to identify the adapter and selects the appropriate initialization profile.

var connection = new ObdConnection(transport);
await connection.Connect();

// Check what was detected
Console.WriteLine(connection.DetectedAdapter?.RawIdentifier); // "ELM327 v1.5"
Console.WriteLine(connection.DetectedAdapter?.Type);          // Elm327

ATI Response Contains	Detected As	Profile Used
"ELM327"	ObdAdapterType.Elm327	Elm327AdapterProfile
"STN"	ObdAdapterType.ObdLink	ObdLinkAdapterProfile
Anything else	ObdAdapterType.Unknown	Elm327AdapterProfile

Explicit Profile

Skip detection by providing a profile to the constructor:

var connection = new ObdConnection(transport, new ObdLinkAdapterProfile());
await connection.Connect(); // uses OBDLink init sequence, no ATI probe

Executing Commands

// Typed command execution
var speed = await connection.Execute(StandardCommands.VehicleSpeed);

// Raw AT/OBD commands
var version = await connection.SendRaw("ATI");      // "ELM327 v1.5"
var protocol = await connection.SendRaw("ATDPN");   // current protocol number
var voltage = await connection.SendRaw("ATRV");     // battery voltage
var pids = await connection.SendRaw("0100");         // supported PIDs [01-20]

Adapter Profiles

Built-in Profiles

Elm327AdapterProfile — Standard ELM327 initialization:

Command	Description
ATZ	Reset adapter
ATE0	Echo off
ATL0	Linefeed off
ATS1	Spaces on
ATH0	Headers off
ATSP0	Auto protocol selection

ObdLinkAdapterProfile — Extends ELM327 with STN optimizations:

Command	Description
(all ELM327 commands)	Standard initialization
STFAC	Reset to STN factory defaults
ATCAF1	CAN auto formatting on

Custom Profiles

Implement IObdAdapterProfile for adapters with special initialization needs:

public class MyAdapterProfile : IObdAdapterProfile
{
    public string Name => "MyAdapter";

    public async Task Initialize(IObdConnection connection, CancellationToken ct = default)
    {
        await connection.SendRaw("ATZ", ct);
        await Task.Delay(500, ct);
        await connection.SendRaw("ATE0", ct);
        await connection.SendRaw("ATSP6", ct);  // force CAN 11-bit 500kbaud
    }
}

var connection = new ObdConnection(transport, new MyAdapterProfile());

Error Handling

ObdException is thrown for adapter-level and protocol errors:

try
{
    var speed = await connection.Execute(StandardCommands.VehicleSpeed);
}
catch (ObdException ex) when (ex.Message.Contains("No data"))
{
    // Vehicle not responding (engine off, unsupported PID, etc.)
}
catch (ObdException ex) when (ex.Message.Contains("Unable to connect"))
{
    // Adapter can't reach the vehicle ECU
}

The connection automatically handles these ELM327 error responses:

Response	Exception Message
NO DATA	No data received from vehicle
UNABLE TO CONNECT	Unable to connect to vehicle
BUS INIT: ...ERROR	Bus initialization error
?	Unknown command
(empty)	Empty response received

Informational prefixes like SEARCHING... and BUS INIT: ...OK are stripped automatically before parsing.

IObdConnection Interface

public interface IObdConnection : IAsyncDisposable
{
    bool IsConnected { get; }
    Task Connect(CancellationToken ct = default);
    Task Disconnect();
    Task<T> Execute<T>(IObdCommand<T> command, CancellationToken ct = default);
    Task<string> SendRaw(string command, CancellationToken ct = default);
}

Note

SendRaw automatically appends a carriage return (\r) to the command before sending it to the transport.