DTC P0300 Random / Multiple Cylinder Misfire Detected; DTC P0301 Cylinder 1 Misfire Detected; DTC P0302 Cylinder 2 Misfire Detected; DTC P0303 Cylinder 3 Misfire Detected; DTC P0304 Cylinder 4 Misfire Detected: Description

Fig 1: Identifying Random / Multiple Cylinder Misfire Detected System Description

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

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 this increase 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 when the crankshaft rotation speed variations exceed predetermined thresholds. If the misfire exceeds the threshold levels, and could cause emission deterioration, the ECM illuminates the MIL and sets a DTC.

DTC TROUBLE DETECTION CONDITION

DTC No.	DTC Detection Condition	Trouble Area
P0300	Simultaneous misfiring of several cylinders detected (2 trip detection logic)	Open or short in engine wire harness Connector connection Vacuum hose connection Ignition system Injector Fuel pressure Mass Air Flow (MAF) meter Engine Coolant Temperature (ECT) sensor Compression pressure Valve clearance Valve timing PCV valve and hose PCV hose connection ECM
P0301 P0302 P0303 P0304	Misfiring of specific cylinder detected (2 trip detection logic)	Open or short in engine wire harness Connector connection Vacuum hose connection Ignition system Injector Fuel pressure > MAF meter ECT sensor Compression pressure Valve clearance Valve timing PCV valve and hose PCV hose connection ECM

HINT:

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.

Reference: Inspection using an oscilloscope

With the engine idling, check the waveform between terminals #1 to #4 and E01 of the ECM connectors.

WAVEFORM REFERENCE

Item	Content
Terminals	#1 to #4 - E01
Equipment Settings	20V/DIV., 100 or 1 ms./DIV.
Conditions	Idling

HINT:

The correct waveform is as shown.

Fig 2: Identifying Waveform