Circuit Description

WARNING: This page is about a different car, the 2003 Lexus GX 470. However, it is still accessible from the selected car via links, so may be relevant.

ECM uses signals provided by crankshaft and camshaft position sensors. If engine speed rate has changed enough to equal a preset number, a misfire is detected and MIL is illuminated. If misfire rate is high enough, and driving conditions will cause catalytic converter damage or overheating, MIL blinks when a misfire is occurring. DTC P0300 is set when misfiring of random cylinders is detected during any particular 200 or 1000 revolutions. DTCs P0301, P0302, P0303, P0304, P0305, P0306, P0307 or P0308 are set when during any particular 200 revolutions of engine, misfiring is detected which can cause catalyst overheating. This causes MIL to blink (one trip detection logic), or, for any particular 1000 revolutions of engine, misfiring is detected which causes a deterioration in emissions. This causes MIL to blink (2 trip detection logic). Possible causes are:

Open or short in wiring.
Poor contact at ECM or component.
Leaking vacuum hoses.
Ignition system malfunction.
Defective fuel injector(s).
Improper fuel pressure.
Defective Mass Airflow (MAF) meter.
Defective Engine Coolant Temperature (ECT) sensor.
Defective engine compression.
Improper valve clearance.
Improper valve timing.
Defective ECM.
Defective PCV piping.