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 the internal PCM functions. Many of the tests are run continuously. Other tests run only under specific conditions, referred to as the 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. The parameters and the values that are considered outside the range of normal operation are listed as the conditions for setting the DTC. When the conditions for setting the DTC are present, 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 the PCM DTCs and the driver alerts that the DTCs trigger. The PCM also saves the data and input parameters when most DTCs are set. This data is stored in the Freeze Frame and Failure Records.

The 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 sets. In some cases there may be exceptions to this structure. Therefore, it is important to read the action taken when the DTC sets and the conditions for clearing the MIL/DTC in the supporting text when diagnosing the system.

The following list describes the general characteristics of each DTC type:
^ The Type A DTCs are emissions related. The PCM performs the following actions at the time of the first fail:
- Illuminates the MIL
- Stores the DTC in memory
- Captures the Freeze Frame and 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 illuminate the MIL
^ Stores the DTC in memory as Failed Last Test
^ Captures the Freeze Frame and Failure Records data
- The PCM performs the following actions at the time of the second fail if the fault is present for 2 consecutive driving cycles:
^ Illuminates the MIL
^ Stores the DTC in memory and the DTC appears in History
^ Updates the Freeze Frame and 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 illuminate the MIL
^ Stores the DTC in memory as Failed Last Test
^ Updates only the Failure Records data
^ Type C DTCs are not emissions related. The PCM performs the following actions at the time of the first fail:
- Does not illuminate the MIL
- Stores the DTC in memory
- Captures the 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 (DIC), depending on how the vehicle is equipped. The lamp or message request occurs at the time of the first fail. The Type C DTCs that do not turn on a lamp or send a message were formerly referred to as Type D.