What does code P0300 mean on a GMC and is it safe to drive?
P0300: Random/Multiple Cylinder 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
The PCM has detected misfires across multiple cylinders. This can cause damage to the catalytic converter if driven for long.
Common causes for your GMC
- Worn spark plugs or ignition coils
- Clogged or bad fuel injectors
- Low compression
- Vacuum leak, bad MAF, or fuel delivery issue
Symptoms
- Check Engine Light (often flashing under load)
- Rough idle, shaking, loss of power
- Possible smell of unburned fuel
Typical fixes
- Replace spark plugs and coils as needed
- Clean or replace fuel injectors
- Fix vacuum/fuel issues
- Compression test if no obvious cause
Repair cost range
For a GMC, repairs for P0300 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 Sierra P0300 on 5.3L LS V8 mirrors Silverado—AFM lifter collapse is the primary cause. When an AFM lifter fails, the PCM may not isolate it to a single cylinder P030X code; instead it logs P0300. Listen for a distinctive ticking at idle that confirms lifter failure. On Acadia 3.6L LLT/LGX V6, the timing chain tensioner can fail, causing cam timing variation and P0300. On Envoy 4.2L Atlas inline-six, the single coil pack cassette (all 6 cylinders on one cassette) fails systematically—a cheap fix that resolves P0300 immediately.
Most commonly affected models