my GMC Sierra T1XX (2019-Present) has a check engine light and code P0301, what should I do?

Learn how to diagnose and fix P0301 cylinder 1 misfire in GMC Sierra T1XX. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, torque wrench, compression tester, multimeter, fuel injector cleaner.
• Ensure the vehicle is parked on a level surface, and the engine is cool.
• Disconnect the battery to prevent any electrical shorts during repair.

2. Inspect and Replace Spark Plug

• Remove the ignition coil from cylinder 1 using the socket set.
• Remove the spark plug from cylinder 1, inspecting for wear, fouling, or damage.
• If necessary, replace the spark plug with a new one that meets OEM specifications (typically AC Delco).
• Reinstall the ignition coil and torque to the manufacturer’s specified value (usually around 15-20 ft-lbs).

3. Check and Replace Ignition Coil (if needed)

• If the spark plug is fine but the code persists, test the ignition coil using a multimeter for resistance.
• If the coil is faulty, remove it and replace it with a new ignition coil compatible with the GMC Sierra.
• Reinstall and ensure all connections are secure.

4. Inspect and Clean Fuel Injector

• Remove the fuel injector from cylinder 1 after relieving fuel pressure.
• Inspect the injector for clogs and clean using a fuel injector cleaner.
• If the injector is faulty, replace it with a new one that matches OEM specifications.
• Reinstall the injector and ensure it is seated properly.

5. Perform Compression Test (if misfire persists)

• Install the compression tester into cylinder 1.
• Crank the engine and record the compression reading.
• If the compression is low, investigate further for potential internal engine issues (like valve problems or piston damage).

6. Reassemble and Reconnect Battery

• Reinstall any components removed during the process.
• Reconnect the battery and ensure all connections are tight.