Circuit Description

WARNING: This page is about a different car, the 2003 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.

Engine Control Module (ECM) uses input signals provided by crankshaft and camshaft position sensors to monitor the changes in crankshaft rotation. If engine speed rate changes enough to equal a preset number, a misfire is detected and Malfunction Indicator Light (MIL) is illuminated. If misfire rate is great enough and driving conditions will cause catalytic converter damage or overheating, the MIL will blink when misfire is occurring. DTC is set when misfiring of random cylinders is detected during any particular 200 revolutions, which can cause catalytic converter to overheat. (This causes MIL to blink; one trip detection logic). DTC is set when misfiring of random cylinders is detected during any particular 1000 revolutions, which causes deterioration of emissions. (This causes MIL to light up; two trip detection logic). Possible causes are:

Open or short in engine wiring harness.
Defective connections at ECM or component.
Disconnected, restricted or damaged vacuum hose(s).
Ignition system malfunction.
Defective fuel injector(s).
Improper fuel pressure.
Defective Mass Airflow (MAF) meter.
Defective Engine Coolant Temperature (ECT) sensor.
Improper engine compression.
Improper valve clearance.
Improper valve timing.
Defective Positive Crankcase Ventilation (PCV) valve hose or connection.
Defective ECM.