how to diagnose a misfire with code P0301 in my GMC Sierra T1XX (2019-Present)

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

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical components.
• Allow the engine to cool before proceeding.

2. Replace Spark Plug

• Remove Engine Cover: If applicable, remove any engine covers obstructing access.
• Disconnect Ignition Coil: Unplug the electrical connector from the ignition coil.
• Remove Ignition Coil: Unscrew and carefully remove the ignition coil from cylinder 1.
• Replace Spark Plug: Use a spark plug socket to remove the old spark plug. Install a new spark plug, ensuring it is gapped correctly according to specifications (typically around 0.040 inches for most applications).
• Reinstall Ignition Coil: Reattach the ignition coil and its connector.

3. Test Fuel Injector

• Remove Fuel Injector Connector: Disconnect the electrical connector from the fuel injector on cylinder 1.
• Test Injector Functionality: Use a multimeter or a noid light to check for power and signal to the injector.
• Replace Injector if Necessary: If the injector is faulty, remove it using an injector puller and install a new one.

4. Perform Compression Test

• Remove Spark Plug: Remove the spark plug from cylinder 1 again if not already done.
• Insert Compression Gauge: Insert a compression gauge into the spark plug hole.
• Crank Engine: Crank the engine a few times to get a reading. Compare the reading to manufacturer specifications.
• Address Low Compression: If low compression is detected, further investigation into piston rings or valves may be necessary.

5. Check for Vacuum Leaks

• Inspect Hoses and Gaskets: Visually inspect all vacuum hoses and gaskets around the intake manifold for cracks or disconnections.
• Use Smoke Test if Necessary: Perform a smoke test to identify any hidden leaks.
• Repair Any Leaks Found: Replace damaged hoses or gaskets.