Description of diagnostic trouble code (DTC) status
The purpose of "Reading off the diagnostic trouble code (DTC) status" is to determine whether the diagnostic trouble code (DTC) is permanent or intermittent. Because of the different criteria for diagnostics, the text message "Diagnostic function not ready" may appear when reading off.
Below is an explanation of the different statuses which may occur.
Diagnostic function not ready
To run a diagnostic, all conditions must be met for the test of the relevant component or sub-system. For certain components/sub-systems, switching on the ignition is sufficient to run the diagnostic. Other require more specific conditions, such as engine speed and temperature etc.
This means for example, that diagnostics requiring an engine speed above 3000 RPM will never run on a stationary car when the engine is only idling. In such cases, where the diagnostic has not run in the present operating cycle, the test message "Diagnostic function not ready" will be displayed.
Permanent
If a diagnostic trouble code (DTC) with a permanent status is stored, the control module has registered a fault and the fault is still present.
Intermittent
If a diagnostic trouble code (DTC) with an intermittent status is stored, the control module has registered a fault and the fault is not present at the moment.
An intermittent electrical fault can be caused by faults in the wiring, components or connectors.
Intermittent functional faults could be caused by mechanical defects in the components.
See also:
• Signal specification