P0302 on a GMC: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

If the check engine light is flashing, stop driving, since a severe misfire can damage the catalytic converter.

What P0302 means on a GMC

On a GMC, P0302 means cylinder 2 is misfiring and not producing power the way it should. Since the code points to one specific cylinder, the fault is usually in cylinder 2's spark plug, ignition coil, or fuel injector rather than a shared system.

Is P0302 common on GMCs?

P0302 shows up on GMC V8 trucks and SUVs like the Sierra and Yukon, as well as the Terrain and Acadia. Spark plugs and coil-on-plug ignition coils are common causes, and on V8 models a failed Active Fuel Management (AFM) lifter can also trigger a cylinder misfire.

Commonly reported on: Sierra, Yukon, Terrain, Acadia.

Symptoms

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

Common causes

most common: Worn or fouled spark plug in cylinder 2
common: Failing ignition coil on cylinder 2
less common: Clogged fuel injector on cylinder 2
less common: Failed AFM lifter on V8 models
less common: Low compression from engine wear

How to fix it

Fix	DIY?	Typical cost
Replace the spark plug in cylinder 2, or all of them	Yes	$40–200
Swap the ignition coil to another cylinder to confirm, then replace it	Yes	$80–300
Replace the faulty fuel injector	Mechanic	$150–600
Have a compression and lifter check done on V8 engines	Mechanic	$100–300