Fault code P0301 – a step-by-step guide to diagnosing and fixing it

This is triggered when the vehicle’s computer detects one or more misfires in engine cylinder 1. It identifies the error by continuously monitoring the rotation speed of the engine crankshaft. Factors such as a lack of fuel or compression, timing problems and sparking disruptions contribute to this ignition fault.

• A worn or faulty spark plug
• Distributor malfunctions
• Damage to the high-voltage wires or coils
• A stretched timing chain or belt, a worn out camshaft, or misaligned timing marks
• A faulty crankshaft, camshaft, MAF or oxygen sensor
• Low fuel pressure or a broken fuel pump on car
• Clogged or malfunctioning fuel injectors
• Vacuum leaks
• A damaged crankcase ventilation hose or defective EGR valve
• A leaking head gasket

• Decreased fuel efficiency
• A loss of engine power
• Stalling when idling
• Jerking or hesitation during acceleration
• Activation of the check engine light
• A pungent fuel smell from the exhaust
• Difficulty starting the engine

• Check all of the trouble codes using an OBD2 scanner for a more accurate diagnosis. Reset the DTC and take the vehicle for a test drive to see whether the check engine light turns on again.
• Inspect the high voltage wires, engine spark plugs, and coils for signs of damage or wear. Make sure there are no loose connectors or ground wires as this can also result in misfiring. If the vehicle is fitted with coil packs, check the pack in the first cylinder for signs of arcing. There may also be an issue with the ignition distributor cap. If water or dirt has got into the component, the rotor could get damaged. Replace the parts if required.
• Check the fuel injectors and fuel pressure. If the injectors are clogged, they will need to be cleaned or “flushed” to remove any build-ups in the system. Cleaning additives can be purchased for this purpose. Low fuel pressure levels can be determined using a gauge tester or diagnostic scanner. For example, DTC P0203 indicates a fuel pump malfunction.
• Clean the valves using specialised cleaning agents.
• It may also be a good idea to do a compression test, although this is a risky procedure. If there are any leaks in the system, these will also need to be addressed. The cylinder head gasket may need to be replaced, or other seals and pipes. Make sure that the clamps are tightened properly.
• Replace any worn valve train parts such as the timing belt or chain and the gears. Adjust the timing belt/chain tension if necessary.
• Test the voltage output of the related sensors using a multimeter.
• If the exhaust fumes smell rotten, check whether the catalytic converter needs to be replaced.