System Description
WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The engine control module (ECM) uses information from the crankshaft position (CKP) sensor and the ignition control module (ICM) in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the ECM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the ECM detects a misfire rate for a specific cylinder sufficient to cause emission levels to exceed mandated standards, DTC P0301, P0302, P0303, or P0304 will set.