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 are 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 are 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 are 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 are 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 are 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. |
