Diagnostic Trouble Codes (DTCs) are categorized into emissions
and non-emissions related types. When a DTC is set, the MIL and Failure data
are utilized by the control modules diagnostic executive according to
the DTC type. Each DTC is set based upon the individual DTCs running and
setting criteria. It is important to 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:
| • | Stores Freeze Frame/Failure records data |
| • | Updates the Failure Records after each ignition cycles first failure |
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 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:
| - | Does not turn on the MIL |
| - | Stores the DTC in memory as Failed Last Test |
| - | Stores Failure Records data |
| • | Second consecutive drive cycle with a failure: |
| - | Stores the DTC in memory as a history DTC |
| - | Stores Freeze Frame data |
| - | Updates Failure Records data |
| • | Second non-consecutive drive cycle with a failure: |
| - | Does not turn on the MIL |
| - | Stores the DTC in memory as Failed Last Test |
| - | Updates Failure Records data |
Non-Emissions Related DTCs
Type C
The following actions occur at the time of a failure:
| • | Does not turn on the MIL |
| • | Stores the DTC in memory as a history DTC |
| • | Stores Failure Records data |
| • | Updates the Failure Records after each ignition cycles first failure |
| • | 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
No actions occur. These DTCs are coded into the control modules software,
but will not run because one of the following reasons:
| • | Associated hardware is not installed with the vehicles emission
package |
| • | The diagnostic is not required for the vehicles emission package |
