Diagnostic trouble codes (DTCs) are categorized into emissions
and non-emissions related types. If a DTC is set, the malfunction indicator
lamp (MIL) and failure data are utilized by the control module diagnostic
executive according to the DTC type. Each DTC is set based upon the individual
DTCs running and setting criteria. Read the Action Taken When the DTC
Sets and Conditions for Clearing the MIL/DTC in the supporting text for
taking appropriate action to each DTC.
Emissions Related DTCs
Type A
The following actions occur at the time of the first failure:
| • | A DTC is stored in memory. |
| • | The Freeze Frame/Failure Records is stored. |
| • | The Failure Records are updated after the first failure of each
ignition cycle. |
Some Type A DTCs will not perform the above actions when the
DTC first detects a failure. Two consecutive failures are required. This allows
systems, such as evaporative emission (EVAP), to accurately identify what
failure exists before setting a DTC and requesting MIL illumination.
Type B
The following actions occur at one of the following times:
| - | The MIL is not turned ON. |
| - | A DTC is stored in memory as a Failed Last Test. |
| - | The Failure Records is stored. |
| • | Second consecutive drive cycle with a failure: |
| - | A DTC is stored in memory as a history DTC. |
| - | The Freeze Frame data is stored. |
| - | The Failure Records is stored. |
| • | Second non-consecutive drive cycle with a failure: |
| - | The MIL is not turned ON. |
| - | A DTC is stored in memory as a Failed Last Test. |
| - | The Failure Records is stored. |
Non-Emissions Related DTCs
Type C
The following actions occur at the time of a failure:
| • | The MIL does not turn ON. |
| • | A DTC is stored in memory as a history DTC. |
| • | The Failure Records is stored. |
| • | The Failure Records are updated after the first failure of each
ignition cycle. |
| • | Some Type C DTCs may also cause an auxiliary service lamp to be
illuminated, and/or display a message to the vehicle operator. |
Type X
Actions did not occur. These DTCs are coded into the control module
software, but will not run for one of the following reasons:
| • | The associated hardware is not installed with the vehicle emission
package. |
| • | The diagnostic is not required for the vehicle emission package. |
