Description of On-Board Diagnostics: Diagnostic Trouble Codes

Diagnostic trouble codes (DTCs)

The control module will store a diagnostic trouble code (DTC) if it detects a fault. The control module can store a maximum of 25 diagnostic trouble codes (DTCs). The number of diagnostic trouble codes (DTCs) varies depending on the type of instrument. If a fault disappears for any reason after the diagnostic trouble code (DTC) has been permanently stored in the control module, information about the fault remains in the control module for a while. For each diagnostic trouble code (DTC) stored, a counter records the total number "fault-free" operating cycles since the diagnostic trouble code (DTC) was stored. If the control module does not register the fault after 10 completed operating cycles, the diagnostic trouble codes (DTCs) are erased automatically. They are "self-erasing".

An operating cycle is defined as where the ignition has been switched off and then on again and the vehicle has then reached a speed in excess of 30 km/h. The ignition must have been on (or the car driven) for longer than 5 minutes.