Note. When 2 or more codes for a misfiring cylinder are recorded repeatedly, but DTC P0300 is not recorded, it indicates that misfires were detected and stored into ECM memory at different times.
Circuit Description
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 during any particular 200 revolutions of engine, misfiring is detected which can cause catalytic converter overheating and/or damage or during any particular 1000 revolutions of engine, misfiring is detected which can cause a deterioration in emission levels. 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.
Diagnostic Aids
When 2 or more codes for misfiring cylinder are recorded repeatedly but no random misfire code is recorded, it indicates misfires were detected and recorded at different times. If misfire cannot be reproduced, reason may be because of driving with lack of fuel, improper fuel, fouled spark plug, etc. Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.