Why DTCS Set

Diagnostic Trouble Codes (DTCs), when set, indicate that the PCM has detected a malfunction in a particular circuit or system. The PCM is programmed with routines or checks that it follows only under prescribed conditions (called Test Conditions). When these conditions exist, the PCM checks certain circuits or systems for a malfunction. These checks are called failure conditions. When the failure conditions are true, a DTC is set. Some DTC(s) alert the driver through the SERVICE ENGINE SOON Malfunction Indicator Lamp (MIL) or a message. Other DTC(s) don't trigger a driver warning. Refer to the DTC TYPE TABLE for a complete list of PCM DTC(s) and what driver alerts they trigger. The PCM also saves data and input parameters when most DTC(s) are set.