Circuit Description

Misfire: The ECM uses the crankshaft position sensor and camshaft position sensor to monitor changes in the crankshaft rotation for each cylinder.

The ECM counts the number of times the engine speed change rate indicates that misfire has occurred. And when the misfire rate equals or exceeds the count indicating that the engine condition has deteriorated, the MIL lights up.

If the misfire rate is high enough and the driving conditions will cause catalyst overheating, the MIL blinks when misfiring occurs.


DTC Detection Condition

Trouble Area


Misfiring of random cylinders is detected during any particular 200 or 1,000 revolutions

•Ignition system •Injector

•Fuel line pressure •Compression pressure •Valve clearance not to specification •Valve timing

•Manifold absolute pressure sensor •Engine coolant temp. sensor

P0301 P0302 P0303 P0304

For any particular 200 revolutions of the engine, misfiring is detected which can cause catalyst overheating (This causes MIL to blink)

For any particular 1,000 revolutions of the engine, misfiring is detected which causes a deterioration in emissions (2 trip detection logic)


When the 2 or more codes for a misfiring cylinder are recorded repeatedly but no Random Misfire code is recorded, it indicates that the misfires were detected and recorded at different times.


12 ECM

12 ECM

Sienna Ecm Diagram
Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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