P0300 on a Mercedes-Benz: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

If the check engine light is flashing, stop driving — a severe misfire can damage the catalytic converter. A steady light is usually safe for a short drive to a shop.

What P0300 means on a Mercedes-Benz

On a Mercedes-Benz, P0300 means the engine computer sees misfires jumping between cylinders instead of on one fixed cylinder. A misfire means a cylinder is not burning its fuel properly, which wastes gas and can damage the catalytic converter if left alone.

Is P0300 common on Mercedes-Benzs?

P0300 appears on Mercedes V6 and V8 engines, such as the M272 in the C-Class and E-Class and the M276 in newer models. Worn spark plugs and ignition coils are the usual causes. Fuel injector issues and vacuum leaks also show up as these engines age.

Commonly reported on: C-Class, E-Class, GLC, GLE.

Symptoms

Check engine light on (flashing if severe)
Rough idle or shaking engine
Loss of power or hesitation
Poor fuel economy

Common causes

most common: Worn or fouled spark plugs
common: Failing ignition coils
common: Clogged or leaking fuel injectors
less common: Vacuum leak
less common: Low compression from engine wear

How to fix it

Fix	DIY?	Typical cost
Replace worn spark plugs	Yes	$100–300
Replace failing ignition coils	Yes	$150–450
Replace faulty fuel injectors	Mechanic	$400–1000
Find and repair vacuum leaks	Yes	$10–100