Circuit Description

WARNING: This page is about a different car, the 2002 Lexus GS 430. 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 is set when misfiring of random cylinders is detected during any particular 200 or 1000 revolutions. Possible causes are:

Open or short in wiring.
Poor connector contact at ECM.
Vacuum hose leaking or misrouted.
Faulty ignition system.
Faulty fuel injector(s).
Improper fuel pressure.
Faulty Mass Airflow (MAF) meter.
Faulty Engine Coolant Temperature (ECT) sensor.
Faulty engine compression.
Improper valve clearance.
Improper valve timing.
Faulty ECM.