Function Explanation (DTC Detection Outline)

WARNING: This page is about a different car, the 2020 Mazda CX-30. However, it is still accessible from the selected car via links, so may be relevant.

The PCM detects the crankshaft rotation speed based on the crankshaft position sensor signal. While the engine is running, the crankshaft rotation speed varies slightly by the effect of combustion at each cylinder, however, the rotation speed changes rapidly if a valve is stuck closed after recovery from cylinder deactivation control. (If valve is stuck closed, engine oil and fuel accumulates in cylinder, and by its ignition there, there is possibility of engine damage) The PCM calculates the frequency of changes (fluctuation rate) in rapid rotation speed for every specified number of crankshaft rotations. When the crankshaft fluctuation rate exceeds a certain value after recovery from cylinder deactivation, the PCM determines that No. 1 or 4 cylinder valve is stuck and stores a DTC.