Enhanced diagnostic information, found in the DTC HISTORY function of the scan tool, is designed to provide the service technician with specific malfunction occurrence information. For each of the first five and the very last diagnostic trouble code (DTC) stored, data is stored to identify the specific DTC, the number of occurrences, and the number of drive cycles since the malfunction first and last occurred. However, if a malfunction is present, the drive cycle counter will increment by turning the ignition switch from on to off. These first five DTCs are also stored in the order of occurrence. The order in which the first five DTCs occurred can be useful in determining if a previous malfunction is linked to the most recent malfunction, such as an intermittent wheel speed sensor which later becomes completely open.

During difficult diagnostic situations, this information can be used to identify malfunction occurrence trends. Did the malfunction only occur once over a large number of drive cycles, indicating an unusual condition present when it occurred? Does the malfunction occur infrequently over a large number of drive cycles, indicating that special diagnostic techniques may be required to identify the source of the malfunction?

If, for example, a malfunction occurred in 1 out of 50 drive cycles, the malfunction is intermittent and has not reoccurred for 49 drive cycles. This malfunction may be difficult or impossible to duplicate and may have been caused by a severe vehicle impact (large pot hole, speed bump at high speed, etc.) that momentarily opened an electrical connector or caused unusual vehicle suspension movement. Malfunction resolution is unlikely, and the malfunction may never recur (check diagnostic aids provided for that DTC).

If, for example, the malfunction occurred in 3 of 15 drive cycles, the odds of finding the cause are still not good, but you know how often it occurs. If the malfunction occurred 10 out of 20 drive cycles, the odds of finding the cause are very good, as the malfunction may be easily reproduced.

By using the additional malfunction data, you can also determine if a malfunction is randomly intermittent or if it has not recurred for long periods of time due to weather changes or a repair prior to this visit. For example, a DTC occurred in 10 of 20 drive cycles but has not recurred in the first 10 of 20 drive cycles. This means the malfunction occurred in 10 of 10 drive cycles but has not reoccurred since. A significant environmental change or a repair may have occurred 10 drive cycles ago. A repair may not be necessary if customer information can confirm a recent repair. If no repair was made, the service technician can focus on diagnosis techniques used to locate problems that are difficult to recreate such as those suggested in diagnostic process or diagnostic aids for the DTC in question.