P0304 on GMC
Cylinder 4 Misfire Detected
P0304 on GMC vehicles indicates cylinder 4 misfire detected. Au7o has documented this code across 5 GMC models — most commonly on Canyon, Savana, Sierra 1500. This code means the engine computer detected a misfire in cylinder number 4 — that cylinder isn't igniting its air-fuel mixture fully or at all. The system detects this by monitoring small changes in crankshaft rotation speed as each cylinder fires. You may feel a rough idle, shaking, hesitation or reduced power, and a persistent misfire can dump unburned fuel into the exhaust and overheat or damage the catalytic converter. Since it's pinpointed to one cylinder, the problem typically lies in that cylinder's spark, fuel, or compression. Typical repair costs on GMC range from $400 to $8,000, depending on the specific model and root cause.
Common Causes of P0304
- •Worn or fouled spark plug in cylinder 4
- •Failed or weak ignition coil on cylinder 4
- •Faulty spark plug wire or boot (where applicable)
- •Clogged, stuck or leaking fuel injector for cylinder 4
- •Vacuum or intake air leak near that cylinder
- •Low compression (worn rings, burnt/leaking valve, head gasket)
- •Damaged wiring or connector at the coil or injector
P0304 on GMC by Model
GMC Canyon(1 issue)
- Active Fuel Management (AFM) Lifter Failure (V6)2015-2025
The 3.6L V6 with Active Fuel Management experiences lifter failure where the AFM lifters collapse, causing misfires and a ticking noise. The collapsing lifter can damage the camshaft lobe if not addressed.
GMC Savana(1 issue)
- AFM Lifter Failure on V8 Vortec/EcoTec3 Engines2010-2025
GMC Savana vans equipped with 4.8L (L20), 5.3L (LM7), and 6.0L (L96) V8 engines with Active Fuel Management suffer the same AFM lifter collapse problem documented across the entire GM full-size truck/van lineup. The collapsible AFM lifters on deactivation cylinders fail between 60,000-120,000 miles, causing misfires, engine ticking, rough idle, and potential engine damage. Commercial Savana vans used for fleet operations are especially vulnerable due to high mileage accumulation and variable maintenance practices. The problem affects all GMT600 platform Savana/Express vans with AFM-equipped engines.
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(2 issues)
- 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.
- 6.0L V8 Excessive Oil Consumption and AFM Lifter Wear2014-2020
The 6.0L L96 V8 gasoline engine in Sierra 2500HD (non-diesel) suffers from Active Fuel Management (AFM) lifter failures similar to the 5.3L in Sierra 1500 — though less frequently due to the higher displacement. More commonly, 6.0L engines exhibit excessive oil consumption (1 qt per 1,000-3,000 miles) from worn valve stem seals and piston rings, particularly between 100,000-150,000 miles. The L96 is a high-output truck engine subjected to heavy towing and payload, which accelerates wear on AFM components.
GMC Yukon(1 issue)
- AFM/DOD Lifter Collapse and Valvetrain Failure2007-2020
The GMC Yukon 5.3L (L83, LC9, LMG) and 6.2L (L94, L86) V8 engines use Active Fuel Management (AFM) cylinder deactivation. The special collapsible AFM lifters on cylinders 1, 4, 6, and 7 fail prematurely, causing misfires, engine ticking, rough idle, and potential catastrophic damage. This is the single most reported mechanical failure on GMT900 (2007-2014) and K2XX (2015-2020) Yukon models. GM issued TSB 18-NA-077 acknowledging the issue. Yukon models used as daily drivers with lots of highway cruising (where AFM activates most) are most susceptible. The VLOM (Valve Lifter Oil Manifold) must also be replaced as it controls oil flow to AFM lifters.
Looking for P0304 on a different make?
View P0304 across all makes →Frequently Asked Questions
What does P0304 mean on GMC?▼
P0304 stands for "Cylinder 4 Misfire Detected." This code means the engine computer detected a misfire in cylinder number 4 — that cylinder isn't igniting its air-fuel mixture fully or at all. The system detects this by monitoring small changes in crankshaft rotation speed as each cylinder fires. You may feel a rough idle, shaking, hesitation or reduced power, and a persistent misfire can dump unburned fuel into the exhaust and overheat or damage the catalytic converter. Since it's pinpointed to one cylinder, the problem typically lies in that cylinder's spark, fuel, or compression. On GMC specifically, this code is documented across 5 models.
What causes P0304 on GMC vehicles?▼
Common causes on GMC: Worn or fouled spark plug in cylinder 4, Failed or weak ignition coil on cylinder 4, Faulty spark plug wire or boot (where applicable), Clogged, stuck or leaking fuel injector for cylinder 4, Vacuum or intake air leak near that cylinder. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0304 on a GMC?▼
Repair costs on GMC range from $400 to $8,000, depending on the specific model and root cause.
Which GMC models have P0304 documented?▼
Au7o has documented P0304 on 5 GMC models: Canyon, Savana, Sierra 1500, Sierra 2500HD, Yukon.