DTC P0300: Engine Misfire Detected: Description

WARNING: This page is about a different car, the 2002 Saturn LW200, 2002 Saturn L200, and 2002 Saturn L100. However, it is still accessible from the selected car via links, so may be relevant.

PCM uses a zero to 5-volt square wave from EI module based off crankshaft position sensor to determine position and RPM of engine at various degrees of crankshaft rotation. PCM bases misfire diagnostics on the principle that crankshaft velocity will increase as each cylinder contributes its power input. Under certain conditions, PCM will monitor crankshaft velocity variation in a series of 200 revolution tests. If 20-100 percent or the revolutions fail, a catalyst damaging misfire has occurred. If 2-19 percent of the revolutions fail, an emission related misfire has occurred. MIL (Service Engine Soon telltale) will flash when an active catalyst damaging misfire occurs on first drive cycle if vehicle speed is more than 30 MPH and MAP is more than 70 kPa. MIL will be on steady if an emission related misfire occurs after 2 consecutive drive cycles. MIL will turn off after 3 consecutive passed drive cycles meeting the same misfire criteria, or 80 passed drive cycles if criteria could not be met. DTC sets when a specific or random cylinder misfire has occurred.