CMP Sensor

CKP Sensor

When the engine misfires, high concentrations of hydrocarbons (HC) enter the exhaust gas. Extremely high HC concentration levels can cause increases in exhaust emission levels. High concentrations of HC can also cause increases in the Three-Way Catalytic Converter (TWC) temperature, which may cause damage to the TWC. To prevent these increases in emissions and to limit the possibility of thermal damage, the ECM monitors the misfire rate. When the temperature of the TWC reaches the point of thermal degradation, the ECM blinks the MIL. To monitor misfires, the ECM uses both the Camshaft Position (CMP) sensor and the Crankshaft Position (CKP) sensor. The CMP sensor is used to identify any misfiring cylinders and the CKP sensor is used to measure variations in the crankshaft rotation speed. Misfires are counted as when the crankshaft rotation speed variations exceed predetermined thresholds. If the misfire rate exceeds the threshold level, and could cause emission deterioration, the ECM illuminates the MIL and sets a DTC.


DTC Detection Condition

Trouble Area


P0301 P0302 P0303 P0304

Simultaneous misfiring of several cylinders detected (2 trip detection logic)

Misfiring of specific cylinder detected (2 trip detection logic)

Open or short in engine wire harness

Connector connection

Vacuum hose connections

Ignition system


Fuel pressure

Mass Air Flow (MAF) meter

Engine Coolant Temperature (ECT) sensor

Compression pressure

Valve clearance

Valve timing

PCV valve and hose

PCV hose connections

Air induction system

When DTCs for misfiring cylinders are randomly set, but DTC P0300 is not set, it indicates that misfires have been detected in different cylinders at different times. DTC P0300 is only set when several misfiring cylinders are detected at the same time.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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