OBD | On-board diagnostics | Part 1: Development and function

Опубликовано: 18 Февраль 2026
на канале: Motorservice Group
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How does on-board diagnostics (OBD) work?
What does it mean when the OBD lamp is flashing?
When does the OBD lamp light up continuously?
How do you read out diagnostic trouble codes?
Find out here.

00:00 Development of OBD
01:42 Explanation: OBD-1, OBD-2, EOBD, EURO 3
02:42 Function of OBD

How the OBD works
If a fault occurs that compromises the exhaust gas quality, a standardised diagnostic trouble code is stored in the fault code memory of the engine control unit. The operating data and environmental conditions at the time the fault occurred are also stored.
If a fault relating to exhaust gas occurs, the OBD lamp (engine check lamp) will light up continuously. If a fault occurs that leads to cylinder shut-off or to damage of the catalytic converter, the OBD lamp will flash. Depending on the severity of the fault, limp-home programs may be activated to protect the engine. If a fault does not recur within a certain time period, the OBD lamp may go out again. The fault remains in the memory in any case. Faults and recorded data can be read out using a scan tool via the diagnostic socket. The diagnostic trouble code specifies the component in question and the type of fault. This makes them useful aids in diagnosing and resolving the fault.

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