Circuit Description

PCM uses pulses from crankshaft position sensor to determine position and RPM of engine at various degrees of rotation. PCM can then base misfire diagnostics on the principle that crankshaft velocity will increase as each cylinder contributes its power input. Under certain conditions, PCM will perform a series of tests to determine misfire percentage on a cylinder based on crankshaft velocity variation. The MIL will flash if an active catalyst damaging misfire occurs (20-100 percent) and will stay on steady if an emission-related misfire (2-19 percent) is present after 2 consecutive trips. The MIL will turn off after 3 consecutive passed trips meeting the same misfire criteria or 80 passed trips if the criteria has not been met.

DTC will set if random misfires have been detected after a series of tests when engine speed is 562-5500 RPM, ECT is 20-244°F (-7 to 118°C), throttle change is not rapid, not in decel fuel cut-off mode, ignition voltage is at 8-15 volts and no TP sensor, CKP, IAT, MAT or ECT DTCs have been set. Misfire diagnostics are continually checked with engine running when these conditions have been met.