P0304 GMC Sierra 1500
Cylinder 4 Misfire Detected · Powertrain Code · High
What is P0304?
Misfire detected in cylinder 4. Typically caused by a worn spark plug, bad ignition coil, faulty fuel injector, or low compression in that cylinder.
When the GMC Sierra 1500 triggers code P0304 (cylinder 4 misfire detected), it typically points to an issue in the powertrain system. This is a high severity code, so address it promptly to avoid further damage or safety concerns. Below you'll find the most common causes, symptoms, and repair options specific to the GMC Sierra 1500.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your GMC Sierra 1500.
Common Causes on GMC Sierra 1500
- Failed spark plug or ignition coil on cylinder 4
- AFM/DFM lifter collapse on cylinder 4 (cylinder 4 is an AFM-deactivated cylinder on 5.3L/6.2L V8)
- Fuel injector clog or electrical failure on cylinder 4
- Low compression due to valve or piston ring issue
Symptoms
- Check Engine Light on (flashing if active misfire)
- Pronounced rough idle
- Vibration felt through steering wheel and seat
- Significant power loss
- Ticking or knocking sound from engine (if lifter failure)
Notes for GMC Sierra 1500
Cylinder 4 is an AFM-deactivated cylinder on GM 5.3L/6.2L V8s — a P0304 misfire on these engines is a classic sign of AFM lifter failure, especially if accompanied by a ticking noise.