SUBJECT/Summary: A vehicle's PCM (powertrain control module) regularly monitors the emissions system for any irregularity and alerts the driver via the Check Engine light when a misfire is detected. When that warning light flashes, it is essential for the driver to take the vehicle to a repair facility immediately to prevent catastrophic damage to the catalytic converter.
PROBLEM: When a cylinder misfires, the air-fuel mixture in the cylinder burns either completely or not at all. On the exhaust stroke, the unburned or partially burned mixture flows toward the catalytic converter. The converter may initially be cooled by the raw fuel. If this cooling drops the temperature below the converter's "light-off" setting of 400 degrees Fahrenheit, the converter cannot reduce emissions efficiently. More important, when this raw air-fuel mixture is ignited in the converter, the temperature naturally rises, and the converter may be permanently damaged.
SOLUTION: Even though the PCM is programmed to detect misfire, set a code, and initiate the Check Engine light, the possibility of catalyst damage from extended misfiring of one or more cylinders led to the EPA's mandating that every manufacturer "Flash" the Check Engine light whenever a misfire occurs that could be "catalyst damaging." The extent of this damage could be complete catalyst failure caused by meltdown.
Bulletin Date: 06/18/09
Bulletin Number: 09-0105
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