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 monitors certain parameters and determines whether or not the values are within an expected range. The parameters and values considered outside the range of normal operation are listed as Conditions for Setting the DTC. When the Conditions for Setting the DTC occur, 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 Diagnostic Trouble Code (DTC) List/Type for a complete list of PCM DTCs and the driver alerts the DTCs trigger. The PCM also saves data and input parameters when most DTCs are set. This data is stored in the Freeze Frame and/or Failure Records.

DTCs are categorized by type. The DTC type is determined by the MIL operation and the manner in which the fault data is stored when a particular DTC fails. 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.

There are different types of DTCs and the action they take when set. Refer to Diagnostic Trouble Code (DTC) Type Definitions for a description of the general characteristics of each DTC type.