my GMC Sierra T1XX (2019-Present) check engine light keeps coming on why

Learn how to diagnose and fix the P0420 check engine light issue in GMC Sierra T1XX. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather all necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal to avoid electrical issues.

2. Address Fault Codes

• Using the OBD-II scanner, note any fault codes that were retrieved.
• Clear the codes and perform a test drive to see if they return.
• If specific codes are indicated (e.g., P0420 for catalytic converter efficiency), focus on the corresponding components.

3. Inspect and Replace Faulty Components

• Gas Cap: If the gas cap is found to be faulty, replace it with a new OEM gas cap. Ensure it clicks securely when tightened.
• Air Filter: If the air filter is dirty, remove the air intake cover, take out the old filter, and install a new one.
• Spark Plugs: If misfire codes are present, remove the ignition coils (if applicable) and spark plugs. Inspect for wear and replace with new OEM spark plugs if necessary.

4. Repair Exhaust Leaks

• If exhaust leaks are detected, use a wrench to tighten any loose connections or replace damaged sections of the exhaust pipe or gaskets.

5. Reconnect Battery and Test

• Reconnect the negative battery terminal.
• Start the engine and let it idle, observing for any unusual behavior or lights.