Question

What causes a P0303 code? 

The P0303 code logs into your PCM when it detects multiple misfires in cylinder 3 of your car. This can be caused by multiple factors, but the most common causes are problems with your ignition system, fuel delivery or mechanical issues such as low compression or an air leak. 

Engine code P0303 signifies that there have been multiple misfires in Cylinder 3. These are some of the other causes that lead to this error code: 

• Defective oxygen sensor 
• Valves that are leaking 
• Bad gas 
• Damaged coil, ignition plug coil pack, or spark plug wires that aren’t connected correctly 
• Defective fuel injector, low or empty fuel, or poor-quality gas 
• Damaged piston rings, valves that aren’t closing correctly, or bad compression 
• The manifold gasket has a leakage 
• Damaged crankshaft 

Once you’ve identified the main cause of the code, it is easy to fix it. Here’s how:

• Inspect for damage. Remove the ignition coil from the engine and inspect it for stains or damage. If the ignition coil has engine oil or stains, clean it with WD-40. If the coil is damaged, go for a replacement. 
• Check the coil packs for signs of wear. 
• Check and replace the spark plugs in all cylinders. 
• Inspect the wiring. Replace the rotor and distributor cap, spark plug wires, or coil pack. 
• Check for damages. If needed, repair fuel issues, mechanical engine issues, and intake air leakages. 
• Inspect the catalytic converter. It may be damaged if the exhaust has an odor of rotten eggs. 
• Check the fuel injectors, which can lead to the P0303 engine code. 
• Check the piston and valves if the cylinder experiences a big drop.