Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
General Information: General Description
The PCM monitors variations in the crankshaft rotation speed to determine if any misfires occurred. When a misfire occurs, the rotational speed of the crankshaft slows down. The PCM then identifies the specific cylinder in which the misfire occurred, and counts individual misfire events. A random misfire (P0300) indicates two or more cylinders are misfiring.
Misfires can be caused by a lack of combustion in a cylinder/s due to: the absence of spark, poor fuel metering, poor compression or timing. Even a small number of misfires may result in excessive exhaust emissions, due to the unburned fuel. Increased misfire rates can cause damage to the catalytic converter.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.