For 1990-2009 cars

Enhanced diagnostic information is found in the DTC HISTORY function of the scan tool. Enhanced diagnostic information provides the service technician with specific malfunction occurrence information. The following occurs for each of the first five diagnostic trouble codes stored and the very last diagnostic trouble code stored:

• | Data is stored to identify the specific DTC

• | The number of diagnostic trouble code occurrences are stored

• | The number of drive cycles since the malfunction first and last occurred are stored. A drive cycle occurs when the ignition is turned to RUN.

• | The drive cycle counter will increment by turning the ignition switch to RUN and OFF if a malfunction is present.

• | The first five diagnostic trouble codes are stored in the order of occurrence. The order of the first five diagnostic trouble codes are used to determine if a previous malfunction is linked to the most recent malfunction, such as an intermittent wheel speed sensor which later becomes completely open.

In difficult diagnostic situations use the above information 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?

Review the following malfunction examples:

1. A malfunction occurred 1 out of 50 drive cycles
2. This malfunction is intermittent and has not recurred for 49 drive cycles
3. A malfunction of this type is difficult or impossible to duplicate
4. The malfunction may have been caused by a severe vehicle impact such as a large pot hole or speed bump at high speed, etc.
5. A severe vehicle impact can momentarily open an electrical connector
6. A severe vehicle impact can cause unusual vehicle suspension movement
7. A malfunction resolution is unlikely
8. The malfunction may never recur
9. Check the diagnostic aids provided for that DTC

Review the following examples:

1. A malfunction occurred 3 out of 15 drive cycles
2. The odds of finding the cause are not good
3. However, the occurrence rate is known
4. A malfunction occurred 10 out of 20 drive cycles
5. The odds of finding the cause of the malfunction are good
6. The malfunction may be easily reproduced

A malfunction that occurs more frequently increases the odds of finding the cause of the malfunction.

Use the additional malfunction data to determine if a malfunction is randomly intermittent. Use the additional malfunction data to determine if it has not recurred for long periods of time due to whether changes or a repair prior to this visit.

Review the following example:

1. A DTC occurred 10 of 20 drive cycles, but has not recurred for 10 drive cycles
2. This means a malfunction occurred 10 of 10 driver cycles, but has not reoccurred since.
3. A significant environment change or a repair may have occurred 10 drive cycles ago
4. If no repair was made, focus on diagnosis techniques used to locate difficult-to-recreate problems. Refer to Diagnostic Aids for the DTC in question.