Diagnostic Trouble Codes (DTCs)

The PCM is programmed with test routines that check the operation of the various systems the PCM controls. Some tests check internal PCM functions. Many tests are run continuously. Other tests run only under specific conditions, referred to as Conditions for Running the DTC. When the vehicle is operating within the conditions for running a particular test, the PCM checks certain parameters and determines whether or not the values are within an expected range. Which parameters and what values are considered outside the range of normal operation are listed as Conditions for Setting the DTC. When the Conditions for Setting the DTC are true, the PCM executes the Action Taken When the DTC Sets. Some DTCs alert the driver via the MIL or a message. Other DTCs do not trigger a driver warning, but are stored in memory. Refer to the DTC Type Table for a complete list of PCM DTCs and what driver alerts they trigger. The PCM also saves data and input parameters when most DTCs are set. This data is stored in Freeze Frame/Failure Records.

DTCs are categorized by type. The DTC type relates to how the MIL operates and how the fault data is stored when a particular DTC tails. In some cases there may be exceptions to this structure. Therefore, reading the Action Taken When the DTC Sets and Conditions for Clearing the MIL/DTC in the supporting text when diagnosing the system is important.

The following list describes the general characteristics of each DTC type:
^ Type A DTCs are emissions related. The PCM performs the following actions at the time of the first fail:
- Turns ON the MIL
- Stores the DTC in memory
- Captures Freeze Frame/Failure Records data
^ Type B DTCs are emissions related. The first fail and any subsequent failures are handled differently.
- The PCM performs the following actions at the time of the first fail:
^ Does not turn ON the MIL
^ Stores the DTC in memory as Failed Last Test
^ Captures Freeze Frame/Failure Records data
- The PCM performs the following actions at the time of the second fail if the fault is active for 2 consecutive driving cycles:
^ Turns ON the MIL
^ Stores the DTC in memory - the DTC will now appear in history.
^ Updates Freeze Frame/Failure Records data
- The PCM performs the following actions at the time of a second failure that is not on a consecutive trip:
^ Does not turn ON the MIL
^ Stores the DTC in memory as Failed Last Test
^ Updates Failure Records data only
^ Type C DTCs are not emissions related. The PCM performs the following actions at the time of the first fail:
- Does not turn ON the MIL
- Stores the DTC in memory
- Captures Failure Records data
- Some Type C DTCs may also turn ON an auxiliary service lamp, and/or cause a message to be displayed on the driver information center (DTC) depending on how the vehicle is equipped. The lamp/message request occurs at the time of the first fail. Type C DTCs that do not turn ON a lamp or send a message were formerly referred to as Type D.