Worn or incorrect spark plugs, or failing ignition coils affecting several cylinders; Vacuum or intake air leak (split hose, intake manifold gasket, brake servo hose) causing a lean mixture; Low or unstable fuel pressure from a weak pump, clogged filter or faulty regulator; Dirty or faulty fuel injectors, or a faulty air flow or manifold pressure sensor giving wrong mixture data; Faulty crankshaft or camshaft position sensor or damaged reluctor wheel giving a false or erratic signal; EGR valve stuck open or leaking, on engines fitted with one; Mechanical fault such as low compression, head gasket leak, worn valve train or incorrect cam timing.

P0300

Random/Multiple Cylinder Misfire Detected.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
3: AreaIgnition system or misfire
00: FaultThe specific fault in that area

What it means

P0300 means the engine control unit has detected misfires that are random or spread across more than one cylinder, rather than being tied to a single cylinder. It sets when the crankshaft speed signal shows repeated irregular acceleration that indicates incomplete combustion. The cause is often something common to all cylinders, such as fuel, air or ignition supply, but several separate faults can also produce it.

Symptoms

Engine running rough or shaking, especially at idle
Hesitation, stumbling or loss of power under acceleration
Engine warning light on, possibly flashing under load
Smell of unburnt fuel or a noticeably rough exhaust note
Hard starting or occasional stalling
Increased fuel consumption

Possible causes

Worn or incorrect spark plugs, or failing ignition coils affecting several cylinderslikely
Vacuum or intake air leak (split hose, intake manifold gasket, brake servo hose) causing a lean mixturelikely
Low or unstable fuel pressure from a weak pump, clogged filter or faulty regulatorlikely
Dirty or faulty fuel injectors, or a faulty air flow or manifold pressure sensor giving wrong mixture datapossible
Faulty crankshaft or camshaft position sensor or damaged reluctor wheel giving a false or erratic signalpossible
EGR valve stuck open or leaking, on engines fitted with onepossible
Mechanical fault such as low compression, head gasket leak, worn valve train or incorrect cam timingrare

How to diagnose

Read all stored and pending codes and note the freeze frame data (engine load, speed, temperature) to see when the misfires occur.
Check for other codes such as fuel trim, air flow, sensor or single-cylinder misfire codes (P0301 onwards) that point to a common cause.
Inspect spark plugs, coil connectors, wiring and vacuum hoses for damage, wear, cracks or loose fittings.
Look at live data: short and long term fuel trims, air flow reading and misfire counters per cylinder to separate lean, rich or ignition faults.
Check for intake leaks, for example by inspecting hoses and gaskets while watching fuel trims change with engine speed.
Test fuel pressure and volume against the manufacturer's specification for that engine.
Check crankshaft and camshaft sensor signals and the wiring to them, and inspect the EGR valve operation where fitted.
If everything else checks out, carry out a compression or leak-down test and verify cam timing, following the procedure for that engine.

How to fix

Replace spark plugs with the correct specification and replace any faulty ignition coils.
Repair or replace leaking vacuum hoses, intake gaskets or other air leaks.
Restore fuel supply by replacing a clogged filter, weak pump or faulty pressure regulator as the test shows.
Clean or replace faulty fuel injectors and replace any faulty air flow or pressure sensor.
Replace faulty crankshaft or camshaft sensors or repair damaged wiring and connectors.
Repair the underlying mechanical fault, such as head gasket, valves or timing, if testing confirms it.

Can I keep driving?

High severity

Avoid driving if the warning light is flashing or the engine is running badly, as raw fuel can overheat and damage the catalytic converter. If the car runs reasonably smoothly, keep journeys short and gentle until it is diagnosed.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

This code for other makes

P0300AudiWorn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable), Incorrect ignition timing, Vacuum leak(s), Low or weak fuel pressure, Improperly functioning EGR system, Defective Mass Air Flow Sensor, Defective Crankshaft and or Camshaft Sensor, Defective Throttle Position Sensor, Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems)