Fault code P0305 – a step-by-step guide to diagnosing and fixing it

Error code P0305 is displayed and the check engine light is on - what does this mean?

The OBD/EOBD system has registered a misfire detection in cylinder 5. This DTC (Diagnostic Trouble Code) indicates problems with combustion in the fifth cylinder, which can lead to incomplete fuel combustion and increased emissions. Error code P0305 is standardized across all manufacturers and occurs in vehicles with at least five cylinders.

What can cause this fault code?

• Defective spark plug in cylinder 5
• Damaged ignition coil or ignition cable
• Blocked or defective fuel injection nozzle
• Low fuel pressure
• Leaking intake valves or exhaust valves
• Worn piston rings or cylinder head gasket
• Clogged air filter
• Defective crankshaft sensor or camshaft sensor
• Loose or corroded cable connections
• Faulty engine control unit (ECU)

What symptoms occur in parallel with fault code P0305?

• Engine running unevenly: Irregular engine running, especially at idling speed
• Loss of power: Noticeable reduction in engine power
• Increased fuel consumption: Engine operates inefficiently
• Exhaust odor: Unburned fuel in the exhaust gas
• Vibrations: Strong vibrations throughout the engine
• Starting problems: Difficult cold starts or uneven engine running
• Exhaust odor: Strong smell of gasoline from the exhaust

How can the problem with error code P0305 be rectified?

• The repair should be carried out systematically to identify the exact cause.
• Check spark plug of cylinder 5 and replace if worn or damaged
• Check ignition coil and ignition cable for continuity and insulation faults, replace defective components
• Clean the fuel injection nozzle of cylinder 5 or replace if defective
• Measure fuel pressure and replace fuel pump and fuel filter if necessary
• Carry out compression test and repair valves, piston rings or cylinder head gasket if values are low
• Check air filter and replace if dirty
• Check crankshaft and camshaft sensor for correct function and replace if necessary
• Check all electrical connections to the ignition system and injection for tightness and corrosion