Circuit Description
WARNING: This page is about a different car, the 2003 Toyota Tundra. However, it is still accessible from the selected car via links, so may be relevant.
The ECM uses the crankshaft position sensor and camshaft position sensor to monitor changes in the crankshaft rotation for each cylinder. The ECM counts the number of times the engine speed changes, which indicates that misfire has occurred. When the misfire rate equals or exceeds the preset count indicating the engine condition has deteriorated, the MIL lights up. If the misfire rate is high enough to cause the catalyst to overheat, the MIL blinks when misfiring occurs.