Enhanced diagnostic information, found in the DTC HISTORY function of the scan tool, provides the service technician with specific malfunction occurrence information. For each of the first five diagnostic trouble codes (DTC) stored and for the last DTC stored, additional data is stored in order to provide the following information:
| • | The number of the DTC |
| • | The number of occurrences |
| • | The number of drive cycles since the malfunction first and last occurred |
A drive cycle occurs when the ignition is turned to RUN and the vehicle is driven faster than 16 km/h (10 mph). However, if a malfunction is present, the drive cycle counter will increment by turning the ignition to RUN, then turning the ignition OFF.
The first 5 diagnostic trouble codes are also stored in the order of occurrence. This order can be useful in determining if a previous malfunction is linked to the most recent malfunction. An example of this is an intermittent steering wheel speed sensor circuit that becomes completely open later.
During difficult diagnosis situations, you can use this information in order to identify malfunction occurrence trends.
| • | If the malfunction only occurs once over a large number of drive cycles, an unusual condition is indicated. |
| • | If the malfunction occurs infrequently over a large number of drive cycles, special diagnostic techniques may be required in order 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 recurred for 49 drive cycles. This malfunction may be difficult or impossible to duplicate. A severe vehicle impact (large pothole, speed bump at high speed) may have had one of the folowing effects:
| • | The impact momentarily opened an electrical connector. |
| • | The impact caused an unusual vehicle suspension movement. |
Malfunction resolution is unlikely, and the malfunction may never recur (refer to the diagnostic aids provided for that DTC).
If the malfunction occurred in 3 out of 15 drive cycles, the odds of finding the cause are still not good, but you know how often the malfunction occurs.
If the malfunction occurred 10 out of 20 drive cycles, the odds of finding the cause are very good, because you may easily reproduce the malfunction.
By using the additional malfunction data, you can also determine if a malfunction is randomly intermittent or if the malfunction has not recurred for long periods of time use to weather changes or a repair prior to this visit.
You can use the additional malfunction data in order to determine if one of the following conditions exist:
| • | A malfunction is randomly intermittent. |
| • | The malfunction has not recurred for a long time. This may be due to changes in weather or a recent repair. |
For example, a DTC could occur in 10 out of 20 drive cycles, but does not recur for the last 10 drive cycles. In other words, that the malfunction occurred 10 out of 10 drive cycles, but has not recurred sincethen. 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, you can focus on diagnostics techniques used to locate difficult-to-recreate problems, such as those suggested in the diagnostic aids for the DTC in question.
