how to fix P0300 random misfire code on GMC Sierra T1XX (2019-Present)

Learn how to diagnose and fix P0300 random misfire in GMC Sierra T1XX. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather tools and materials: OBD-II scanner, socket set, torque wrench, fuel pressure gauge, and replacement parts as necessary.
• Disconnect the negative battery terminal to ensure safety.

2. Inspect and Replace Spark Plugs

• Remove the ignition coil harness and unbolt the ignition coils using the socket set.
• Pull out the spark plugs using a spark plug socket; inspect and replace if worn or damaged.
• Torque new spark plugs to the manufacturer's specifications (typically around 15-20 ft-lbs).

3. Check and Replace Ignition Coils

• If the ignition coils show signs of damage, replace them:
  • Remove the old ignition coils and install new ones, ensuring they are seated correctly.
  • Reconnect the ignition coil harness securely.

4. Inspect and Clean Fuel Injectors

• If fuel injectors are suspected to be clogged:
  • Disconnect the fuel lines and electrical connectors from the injectors.
  • Use a fuel injector cleaning kit to clean the injectors or replace them if necessary.
• Ensure that the fuel injector O-rings are replaced to prevent leaks.

5. Check for Vacuum Leaks

• Inspect vacuum lines for cracks or disconnections; replace any damaged lines.
• Use a smoke machine or carburetor cleaner to check for leaks around the intake manifold.

6. Compression Test

• If misfires persist, perform a compression test:
  • Remove the spark plugs and insert the compression gauge into the cylinder.
  • Crank the engine and record the readings for each cylinder.
  • Compare the values; if any cylinder shows significantly lower compression, further investigation is needed.