obd-diag¶

OBD-II diagnostics for Linux with ELM327-compatible adapters, as a command line tool and as a desktop application. obd-diag reads trouble codes and explains them in English or German, shows readiness, freeze frame, VIN and live data, and can record the entire communication with the adapter.

Important

Read-only, clearing locked. The only writing command is clearing the trouble codes (mode 04); it is switched off until it is explicitly enabled. Reading has so far been verified on one vehicle (Mercedes A 180 d, W177, see First test at the car). Without hardware, the response handling is verified against the ELM327 datasheet, real traces from other programs and python-OBD (Testing without a car).

What obd-diag can do¶

Function	OBD service	Page
Read trouble codes (stored, pending, permanent) with plain text	Mode 03, 07, 0A	Reading and clearing trouble codes
Explain codes without a catalog text online (optional, unverified)	–	Explaining trouble codes online
Readiness (monitors, check engine light)	Mode 01 PID 01	User interface
Readiness assistant: incomplete tests of this drive, which drive completes them	Mode 01 PID 01, 41	Readiness assistant
Used-car check: were the codes cleared recently?	Mode 01, 0A	Used-car check
Freeze frame for the triggering trouble code	Mode 02	OBD-II services
Read the VIN and decode it offline	Mode 09 PID 02	VIN decoding
Control units: name, calibration ID, CVN, monitoring counters	Mode 09	Control units and test results
Test results of the self-tests with limits	Mode 06	Control units and test results
Live data: 140 values from 87 PIDs, CSV recording	Mode 01	Live data
Save and compare sessions, PDF report, CSV	–	Sessions, report and trace
Clear trouble codes (locked)	Mode 04	Reading and clearing trouble codes

What obd-diag cannot do: control units outside the standardised emissions diagnostics (airbag, ABS, comfort), coding, flashing, service functions. This is a deliberate decision (ADR 0002: Read-only, with an allowlist in the driver).

Where to start¶

At the car: Installation, then Adapter and connection and First test at the car.
Try it without a car or adapter: Try it without a car.
Understand what goes over the wire: Communication with the ELM327 and Response formats, every command with its datasheet page in the Command reference. A real trace, explained line by line: Trace from the W177, line by line.
Contribute: Contributing and rules and Testing without a car.

This documentation exists in English and German (link at the top of the sidebar). The program itself speaks both languages: Language.