Chevrolet code

P0300 on a Chevy

P0300

In plain words: More than one cylinder, or no single one, is misfiring.
Standard name: Random/Multiple Cylinder Misfire Detected
System: Ignition and misfire

General information, not a mechanic's diagnosis: have a mechanic confirm before any repair.

What the computer saw

P0300 on a Chevrolet is the standard generic code: random or multiple cylinder misfires. The computer saw the crankshaft stumble in more than one cylinder, or could not pin it to one.

Chevy V8s with cylinder deactivation

Many Chevrolet and GM V8 trucks and SUVs shut off half their cylinders on the highway to save fuel (Active Fuel Management or Dynamic Fuel Management).

Tell the shop whether the misfire shows at highway cruise, when cylinders shut off, or at idle and under load, when all of them run.

Likely causes, most common first

Worn spark plugs. The first thing to check at high mileage.
Weak ignition coils. Swapping coils between cylinders shows whether the misfire follows the coil.
A vacuum leak or lean mixture. A lean code beside it points here.
Fuel delivery. Injectors or fuel pressure.
A mechanical problem. Such as a lifter or low compression; found with a compression test or an inspection.

What you can note yourself

Note whether the light is steady or flashing, and tell the shop.
Note any cylinder code stored with it, and whether the misfire happens on the highway, when cylinders shut off.

What to tell the shop

Every code and whether the light flashed.
Whether the misfire shows at idle, under load or at highway cruise.

This page gives no verdict on whether a car is safe to drive; a mechanic can.