What does code P0304 mean on a GMC and is it safe to drive?
P0304: Cylinder 4 Misfire Detected. Here's what it means on your GMC, what usually causes it, what repairs typically cost, and how safe it is to keep driving.
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What this code means
Misfire confirmed on cylinder 4. On 4-cylinder engines, this is the last cylinder—check coil and plug first, then injector, then compression.
Common causes for your GMC
- Worn spark plug on cylinder 4
- Failed ignition coil on cylinder 4
- Faulty or clogged fuel injector
- Low compression or valve issue
Symptoms
- Check Engine Light
- Rough idle and shaking
- Poor acceleration or power loss
Typical fixes
- Replace spark plug and COP coil on cylinder 4
- Clean or replace fuel injector
- Compression and leak-down test if basic parts check out
Repair cost range
For a GMC, repairs for P0304 often fall between $150 and $900, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on GMC
GMC 5.3L P0304 is a non-AFM cylinder on the Sierra. On the 2.4L Ecotec Terrain, cylinder 4 misfires often indicate timing chain stretch—a known weakness. On Canyon 2.8L Duramax diesel, P0304 means a failed fuel injector on cylinder 4.
Most commonly affected models
Sierra 5.3L 2007–2014Terrain 2.4L 2010–2017Canyon 2.8L 2015–2022