The Diagnostic Executive has the capability of alerting the driver of potentially damaging levels of engine misfire that could damage the catalyst. If this type of condition is detected, the MIL is commanded to flash on/off once per second during the actual misfire condition.
The Misfire Diagnostics represents a special type of trouble code diagnostics. Each time a misfire is detected, the engine load, engine speed and coolant temperature at that moment are recorded and the last reported set of Conditions: are stored in Freeze Frame when the key is turned off. During the next few key on/off cycles, the stored Conditions: are used as a reference for similar conditions.
If an emissions threatening misfire occurs for two consecutive trips, the PCM treats the fault as a normal Type B trouble code (it turns on the MIL and stores a code). However if a misfire is detected on two non-consecutive trips, the stored Conditions: are compared with the current conditions. If a misfire occurs on a second non-consecutive trip under the similar Conditions: listed below, the MIL is illuminated: