What causes P0300 on a GMC Sierra 1500?

Common causes of P0300 on GMC Sierra 1500: AFM/DOD lifter collapse causing intermittent valve deactivation failure on cylinders 1, 4, 6, or 7; Worn or carbon-fouled AC Delco spark plugs beyond 100k-mile interval; Failed ignition coil pack on one or more cylinders (common on 5.3L Vortec); Cracked or leaking intake manifold gasket allowing unmetered air into cylinders; Worn valve springs losing tension causing inconsistent valve timing at idle.

P0300

P0300 GMC Sierra 1500

Q: How much does it cost to fix P0300 on a GMC Sierra 1500?

Fixes for P0300 on GMC Sierra 1500 include: Replace all 8 AFM lifters and install DOD delete kit to prevent recurrence, Replace all 8 spark plugs with AC Delco 41-110 Iridium (OE spec), Replace failed ignition coil(s) with AC Delco D513A and inspect boots for carbon tracking, Replace upper intake manifold gasket set and inspect for vacuum leaks, Replace weak valve springs with updated GM part number springs.

Random/Multiple Cylinder Misfire Detected · Powertrain Code · High · Repair: Moderate

What is P0300?

The ECM has detected misfires occurring in multiple or random cylinders. Common causes include worn spark plugs, faulty ignition coils, vacuum leaks, low fuel pressure, or a failing catalytic converter.

When the GMC Sierra 1500 triggers code P0300 (random/multiple cylinder 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.

This repair is rated moderate, meaning some experience and specialty tools required.

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

AFM/DOD lifter collapse causing intermittent valve deactivation failure on cylinders 1, 4, 6, or 7
Worn or carbon-fouled AC Delco spark plugs beyond 100k-mile interval
Failed ignition coil pack on one or more cylinders (common on 5.3L Vortec)
Cracked or leaking intake manifold gasket allowing unmetered air into cylinders
Worn valve springs losing tension causing inconsistent valve timing at idle

Symptoms

Rough idle with noticeable engine vibration
Engine shaking or stumbling under load
Loss of power during acceleration
Check engine light flashing intermittently
Poor fuel economy
Hesitation or stumble on acceleration

Recommended Fixes

Replace all 8 AFM lifters and install DOD delete kit to prevent recurrence

Replace all 8 spark plugs with AC Delco 41-110 Iridium (OE spec)

Replace failed ignition coil(s) with AC Delco D513A and inspect boots for carbon tracking

Replace upper intake manifold gasket set and inspect for vacuum leaks

Replace weak valve springs with updated GM part number springs

Notes for GMC Sierra 1500

AFM/DOD lifter failure is the most common cause on 5.3L and 6.2L engines; consider AFM delete during repair.

P0300 GMC Sierra 1500

What is P0300?

Common Causes on GMC Sierra 1500

Symptoms

Notes for GMC Sierra 1500

Check GMC Sierra 1500 Specs