What does code P0306 mean on a GMC and is it safe to drive?
P0306: Cylinder 6 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.
What this code means
Misfire on cylinder 6, found on V6 and V8 engines. On transversely-mounted V6 engines the rear bank cylinders (including cylinder 6) often have higher labor costs due to access difficulty.
Common causes for your GMC
- Worn spark plug on cylinder 6
- Failed coil-on-plug
- Fuel injector fault
- Low compression
Symptoms
- Check Engine Light, may flash under load
- Rough idle or vibration
- Hesitation and power loss
Typical fixes
- Replace spark plug and COP coil on cylinder 6
- Replace or clean injector on cylinder 6
- Compression and leak-down test if no improvement
Repair cost range
For a GMC, repairs for P0306 often fall between $150 and $1200, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on GMC
GMC 5.3L P0306 is a non-AFM cylinder. Standard coil and plug diagnosis applies on Sierra and Yukon. On the 3.6L DI V6 Acadia, P0306 rear-bank cylinder may indicate carbon buildup. The 3.6L intake valves benefit from periodic walnut blasting past 80k miles.
Most commonly affected models