P0302 on GMC
Cylinder 2 Misfire Detected
P0302 on GMC vehicles indicates cylinder 2 misfire detected. Au7o has documented this code across 2 GMC models — most commonly on Sierra 1500, Sierra 2500HD. This code means the engine computer has detected a misfire specifically in cylinder 2, meaning that cylinder isn't completing combustion properly on some firing events. The computer watches tiny variations in crankshaft speed to spot when a cylinder fails to fire, and a misfire means the air-fuel mixture isn't igniting correctly — usually from a spark, fuel, or compression problem in that cylinder. You may feel a stumble, rough idle, shaking, loss of power, or a flashing check-engine light, and persistent misfires can damage the catalytic converter. Because it names a single cylinder, the fault is often a component serving just cylinder 2, like its coil, plug, or injector. Typical repair costs on GMC range from $400 to $3,500, depending on the specific model and root cause.
Common Causes of P0302
- •Worn or fouled spark plug (cylinder 2)
- •Failed ignition coil or coil-on-plug (cylinder 2)
- •Clogged or faulty fuel injector (cylinder 2)
- •Vacuum or intake air leak affecting that cylinder
- •Low compression (worn rings, burnt/bent valve, head gasket)
- •Damaged spark plug wire or boot (if equipped)
- •Carbon-tracked or cracked coil/plug causing spark loss
- •Faulty PCM/ECM driver (rare)
P0302 on GMC by Model
GMC Sierra 1500(1 issue)
- Direct Injection Carbon Buildup on Intake Valves2014-2023
Direct injection engines do not spray fuel over the intake valves like port injection systems, allowing carbon deposits from oil and blow-by gases via the PCV system to accumulate on intake valve backs and ports. Over time, this buildup restricts airflow causing performance and efficiency loss. The 5.3L and 6.2L engines with direct injection are susceptible to this issue typically after 60,000-100,000 miles.
GMC Sierra 2500HD(1 issue)
- LML Duramax EGR Cooler and EGR Valve Failure2011-2016
The LML Duramax EGR (exhaust gas recirculation) cooler is prone to coolant leaks internally, allowing coolant to enter the intake manifold and combustion chambers. Coolant in the intake causes white smoke, rough running, and potential hydrolocking of cylinders. The EGR valve also sticks open or closed from carbon buildup, causing rough idle, black smoke, and check engine lights. The EGR cooler failure can occur as early as 60,000 miles on trucks used in stop-and-go driving. GM issued multiple TSBs addressing EGR cooler design improvements.
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View P0302 across all makes →Frequently Asked Questions
What does P0302 mean on GMC?▼
P0302 stands for "Cylinder 2 Misfire Detected." This code means the engine computer has detected a misfire specifically in cylinder 2, meaning that cylinder isn't completing combustion properly on some firing events. The computer watches tiny variations in crankshaft speed to spot when a cylinder fails to fire, and a misfire means the air-fuel mixture isn't igniting correctly — usually from a spark, fuel, or compression problem in that cylinder. You may feel a stumble, rough idle, shaking, loss of power, or a flashing check-engine light, and persistent misfires can damage the catalytic converter. Because it names a single cylinder, the fault is often a component serving just cylinder 2, like its coil, plug, or injector. On GMC specifically, this code is documented across 2 models.
What causes P0302 on GMC vehicles?▼
Common causes on GMC: Worn or fouled spark plug (cylinder 2), Failed ignition coil or coil-on-plug (cylinder 2), Clogged or faulty fuel injector (cylinder 2), Vacuum or intake air leak affecting that cylinder, Low compression (worn rings, burnt/bent valve, head gasket). Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0302 on a GMC?▼
Repair costs on GMC range from $400 to $3,500, depending on the specific model and root cause.
Which GMC models have P0302 documented?▼
Au7o has documented P0302 on 2 GMC models: Sierra 1500, Sierra 2500HD.