Function Explanation (DTC Detection Outline)

• The PCM detects the crankshaft rotation speed based on the crankshaft position sensor signal. If there is a small amount of fluctuation in crankshaft rotation speed due to the effect of combustion of each cylinder while the engine is rotating and a misfire occurs in any of the pistons, the crankshaft rotation speed will change suddenly. The PCM adds the number of changes in sudden rotation speed (misfire rate) to each specified crankshaft rotation speed, and if the misfire rate exceeds a certain value, a DTC is recorded.

Fig 1: Crankshaft Rotation Speed Fluctuation Waveform

Courtesy of MAZDA MOTORS CORP.