Self-Diagnostic System: OBD-II

ECM detects malfunctions related to engine sensors or actuators. OBD-II monitors emission related components and can store Diagnostic Trouble Codes (DTCs), first trip DTCs, freeze-frame data, first trip freeze-frame data and System Readiness Test (SRT) information. Using a scan tool, this data and DTC information can be retrieved to assist in diagnosing problems.

When a malfunction is detected for the first time, the first trip DTC and first trip freeze frame data are stored in Engine Control Module (ECM) memory. However, in most instances, MIL will not be illuminated. If the same malfunction is detected on the next trip (under similar conditions), MIL will be illuminated and a DTC is stored (2nd trip detection logic). If a misfire or fuel system malfunction should occur during first trip, MIL may be illuminated or flash. DTC and freeze-frame information will be stored to aid in diagnostics by specifying operating conditions when DTC was set.