Classification of diagnostic trouble codes

In principle, malfunctions can be classified in two categories, intermittent or permanent.

Permanent malfunctions. 

The easiest malfunctions to identify and confirm as a malfunction are the permanent malfunctions. A permanent malfunction is a malfunction when something has "broken" and remains like that until it is repaired.

Intermittent malfunctions. 

The intermittent malfunctions are, as opposed to the permanent malfunctions, are both difficult to identify and confirm. The malfunction exists but is neither active nor present all the time. The malfunction comes and goes briefly under very rare conditions.

For the intermittent malfunctions, the degree of intermittence can also be determined, that is, how intermittent the malfunction is (how often/seldom the malfunction appears).

HINT: For assessment of intermittence, stored counters are used together with the diagnostic trouble code. 

Common permanent malfunction causes are: 

• Open circuits or short-circuits on cables or in connectors caused by mechanical damage, vibrations, corrosion, oxidation, moisture, etc.

Common intermittent malfunction causes are: 

• Loose connections or contact resistance caused by vibrations, corrosion, oxidation, moisture, etc.
• Brief short-circuits to both ground and voltage caused by damage to cables, moisture in connectors, etc.
• Electro-magnetic interference.

Malfunction causes may be both electrical, mechanical or related to software.

Intermittent malfunctions (or malfunctions that occur under unknown conditions) may also be malfunctions that only occur during certain operation or ambient conditions.

E.g., that the window or seat for some reason jams in its end-position when using automatic function, or that the climate control unit supplies poor heat in a certain position when it rains outside.