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P0300 fault code: what it means

P0300: Random or multiple-cylinder misfire. A flashing check light means misfire bad enough to damage the catalytic converter.

Engine and gearbox (powertrain) · Costly if missed

Usual causes, most likely first

  1. worn spark plugs
  2. failing ignition coils
  3. vacuum leak
  4. low fuel pressure or dirty injectors

P0300 by make

Audi

Random or multiple cylinder misfire. On TSI/TFSI: coils and plugs first, then PCV/air leaks, carbon on the intake valves and fuel faults.

Usual causes: failed ignition coil(s) or worn spark plugs; PCV / breather valve or other air leak; carbon build-up on intake valves (direct injection); injector fault or low fuel pressure

BMW

Random or multiple cylinder misfire. On BMW coils and plugs are the usual fault; oil in plug wells from a leaking rocker cover gasket kills coils.

Usual causes: ignition coil (oil contamination from rocker cover gasket); worn spark plugs; leaking injectors (N54 / N55 piezo); vacuum leak from crankcase vent valve

Ford

Random or multiple misfires. On Falcon usually ignition coils or plugs; on EcoBoost check for coolant getting into the cylinders.

Usual causes: worn spark plugs or failed coil packs; coolant intrusion (EcoBoost); vacuum leak

Haval

Random/multiple cylinder misfire. A flashing check light means ease off and get it checked.

Usual causes: worn spark plugs; failed ignition coil; carbon build-up on direct-injection intake valves; injector fault

Holden

Random or multiple misfires. On direct-injection 3.0 and 3.6 V6 (VE/VF Commodore, Captiva 3.0) carbon on the intake valves is a known cause, with hard starts.

Usual causes: carbon build-up on intake valves (SIDI V6); worn spark plugs or ignition coils; timing chain stretch upsetting cam timing

Honda

Random or multiple cylinder misfire. On Honda engines with screw-adjusted valves, tight exhaust valve clearance is a common and often missed cause, especially cold.

Usual causes: worn spark plugs; tight valve clearance (valve adjustment due); weak ignition coil; vacuum leak

Hyundai

Random misfires on several cylinders. On Theta II / Nu / Gamma GDI engines listen for knocking: misfires can be an early sign of bearing failure.

Usual causes: worn spark plugs or failing ignition coils; carbon build-up on intake valves (GDI); con-rod bearing failure on Theta II / Nu engines; vacuum leak or fuel delivery fault

Jeep

Random/multiple cylinder misfire. On the 3.6 Pentastar check whether the misfires sit on one bank; a flashing light means stop driving hard.

Usual causes: worn spark plugs or failed coil pack; left cylinder head valve seat wear (early 3.6 Pentastar); vacuum leak; low fuel pressure

Kia

Random misfires on several cylinders. On Theta II / Nu engines check for knocking.

Usual causes: worn spark plugs or failing ignition coils; carbon build-up on intake valves (GDI); con-rod bearing failure (Theta II / Lambda); leaking injectors

Lexus

Random/multiple cylinder misfire. On IS250/GS300 (4GR/3GR direct injection) usually carbon on the intake valves; rough idle once warm.

Usual causes: carbon build-up on intake valves (direct-injection V6); worn spark plugs or ignition coils; clogged EGR on CT200h; intake leak

Mazda

Random or multiple-cylinder misfire. On SkyActiv-G petrols worn spark plugs and ignition coils are the usual cause; flashing engine light means stop and fix before the cat is damaged.

Usual causes: worn spark plugs; failing ignition coil(s); fuel injector fault; air leak or sensor signal fault (MAF, CKP)

Mercedes-Benz

Random or multiple cylinder misfire. On Mercedes petrols usually ignition coils or plugs; can damage the catalytic converter if left.

Usual causes: worn spark plugs; failing ignition coil(s); MAF sensor or fuel pressure fault; faulty fuel injector

MG

Random/multiple cylinder misfire.

Usual causes: worn spark plugs; failed ignition coil; vacuum leak; injector fault

Mini

Random or multiple cylinder misfire. On Mini check coils and plugs first; direct injection Cooper S engines also suffer intake valve carbon build-up.

Usual causes: ignition coil; worn spark plugs; fuel injector (N14 / N18 direct injection); Valvetronic fault

Mitsubishi

Random or multiple misfire. On Mitsubishi petrols, if ignition checks out, carbon on the intake valves is a known cause.

Usual causes: worn spark plugs or failing ignition coils; carbon on intake valves; vacuum leak; injector fault

Nissan

Random or multiple cylinder misfire. On VQ V6s ignition coils and spark plugs are the usual culprits.

Usual causes: failed ignition coil; worn spark plugs; oil in spark plug tubes from leaking valve cover seals; cam timing or cam sensor fault (with P0011/P0021)

Skoda

Random or multiple cylinder misfire. On TSI/TFSI: coils and plugs first, then PCV/air leaks, carbon on the intake valves and fuel faults.

Usual causes: failed ignition coil(s) or worn spark plugs; PCV / breather valve or other air leak; carbon build-up on intake valves (direct injection); injector fault or low fuel pressure

Subaru

Random or multiple-cylinder misfire. On EJ25 check for head gasket coolant leaks before buying coils.

Usual causes: worn spark plugs or failing ignition coils; oil in spark plug tubes from leaking valve cover seals (EJ25); EJ25 head gasket leak (coolant into cylinder); vacuum leak or fuel delivery fault

Suzuki

Random/multiple cylinder misfire.

Usual causes: worn spark plugs; failed ignition coil; vacuum leak; EGR valve sticking open

Toyota

Random or multiple cylinder misfire. On 2ZR-FXE hybrids a clogged EGR system is a big cause and can lead to head gasket failure if left.

Usual causes: clogged EGR cooler/passages (hybrids); worn spark plugs or failing ignition coils; intake/vacuum leak; head gasket failure

Volkswagen

Random or multiple cylinder misfire. On TSI/TFSI: coils and plugs first, then PCV/air leaks, carbon on the intake valves and fuel faults.

Usual causes: failed ignition coil(s) or worn spark plugs; PCV / breather valve or other air leak; carbon build-up on intake valves (direct injection); injector fault or low fuel pressure

Volvo

Random/multiple cylinder misfire.

Usual causes: worn spark plugs; failed ignition coil; vacuum leak; low fuel pressure

What the repair usually costs

Not sure what P0300 means on your car? Ask Credov.

Before you clear it

Write the code down or photograph the scanner first. A code that comes straight back after clearing points to a fault that is still there. A car whose codes were cleared just before you arrived may be hiding one: the scanner's readiness monitors show "not ready" for a while after codes are cleared.

Researched by Credov from manufacturer and workshop sources. A fault code points to where a fault may be; a workshop confirms it with a diagnosis. Browse all fault codes.