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

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

Solution

1. Preparation

• Gather tools and ensure the vehicle is parked on a flat surface with the engine off.
• Disconnect the negative battery terminal to ensure safety.

2. Replace Spark Plugs

1. Remove the engine cover if applicable.
2. Use a socket set to carefully remove the spark plug wires or ignition coils.
3. Using a spark plug socket, remove each spark plug.
4. Inspect the old spark plugs for wear or deposits; replace them with new ones if necessary (consult manufacturer specifications for type and gap).
5. Install new spark plugs and torque them to the manufacturer’s specifications (usually around 13-20 lb-ft).
6. Reattach the ignition coils or spark plug wires.

3. Inspect and Replace Ignition Coils

1. If misfires persist after replacing spark plugs, test ignition coils using a multimeter (check primary and secondary resistance).
2. If faulty, disconnect the wiring harness and remove the ignition coils.
3. Install new ignition coils ensuring a secure fit and reconnect the wiring harness.

4. Fuel Injector Cleaning or Replacement

1. If the issue continues, remove fuel injectors for inspection.
2. Use a fuel injector cleaning kit or ultrasonic cleaner to clean injectors.
3. If injectors are clogged or damaged, replace them with new units.

5. Check for Vacuum Leaks

1. Inspect all vacuum lines for cracks or disconnections.
2. Use a smoke machine to detect leaks or spray soapy water around suspected areas to look for bubbles during engine operation.
3. Replace or repair any faulty vacuum lines.