OBD fault codes: information for diagnosis, not a verdict on a part

Useful to know

OBD is an on-board diagnostic system that monitors components and systems related to engine emissions and performance. The EPA describes how electronics monitor data, detect malfunctions, and can alert the driver via an indicator. [1]

Reading recorded code gives reference information. It does not automatically mean that every sensor name in the code text is final proof of a faulty particular sensor. Diagnostics should track the cause and condition of the system.

Practically write down the exact code and conditions under which the problem occurred, instead of translating it into a parts purchase list. Distinguish observation from conclusion: "code recorded" and "specific failure confirmed" are different claims.

The source is an EPA historical technical document for U.S. OBD requirements. We use it for the basic principle, not as an up-to-date instruction for a Bulgarian technical review or a universal repair procedure.