System Diagnosis

The Electronic Control Module (ECM) is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction that may affect vehicle emissions is detected during 2 sequential drive cycles, the ECM will illuminate the Malfunction Indicator Light (MIL) on the instrument panel and a corresponding Diagnostic Trouble Code (DTC) will be stored in ECM. If a misfire is detected, MIL will illuminate and DTC will be stored in ECM immediately after fault is detected. If misfire is severe enough to cause catalytic converter damaged, MIL will blink. MIL will continuously blink until danger to catalytic converter has passed. To retrieve stored DTC(s), see RETRIEVING DIAGNOSTIC TROUBLE CODES  .

MIL will turn off if the fault that turned it on is not detected for 3 sequential drive cycles, but DTC will remain in ECM memory. If fault that set DTC is not detected for 40 drive cycles, DTC will be erased from ECM memory. If battery is disconnected, all DTCs and freeze frame data will be erased from ECM. As a bulb check, MIL will also illuminate for about 5 seconds when ignition is turned on.

DTCs will be recorded at various operating times and conditions. Some DTCs require operation of sensor or switch for 5 seconds, while other components require operation for 5 minutes or longer at normal operating temperature, vehicle speed, and load. Therefore, when verifying repair, some DTCs may not set in a service bay and may require road testing to duplicate the conditions under which the code will set.