Diagnostic Functions: Diagnostic Trouble Codes

DTC Functions


If the control unit detects a fault it stores a diagnostic trouble code and the SRS warning lamp comes on. The only time the warning lamp does not come on is when the wire between the control unit and the combination instrument has short circuited to ground, or the bulb is faulty. When the ignition is switched on, the lamp should come on for about 3 seconds and then go off if no diagnostic trouble code is made.

The control unit can store up to 10 different diagnostic trouble codes. If, for any reason, a fault disappears after the diagnostic code registers it in the control unit as permanent, the information concerning the fault remains stored in the control unit.

Each diagnostic trouble code has a total of 4 diagnostic clocks which store information about when the fault started and subsequently ended. Absolute start and end times relate to the total time the system has been switched on the ignition.

Relative start and end times show the times when the fault occurred or disappeared when the ignition was last switched on. Absolute times show days and relative times show hours, minutes and seconds. If the fault occurs again the end time is reset and the diagnostic trouble code counter (counter 2) registers the first occurance.

Each diagnostic trouble code has a counter (counter 1); if the fault is passive (intermittent), the counter value is 0, if the fault is active (permanent), the value is greater than 0. The counter is used in trouble-shooting to see if the fault remains or disappears.

The diagnostic trouble code status display is constantly updated and only changes to an intermittent fault, when the fault is inactive. If the fault is passive and becomes active, the diagnostic trouble code status display changes to register it as permanent.