how to fix P0420 code on GMC Sierra T1XX (2019-Present)

Learn how to diagnose and fix P0420 code in GMC Sierra T1XX. Step-by-step guide with diagnostic procedures and repair instructions for exhaust issues.

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the battery to ensure safety while working on electrical components.
• Raise the vehicle securely on jack stands.

2. Inspect and Replace Oxygen Sensors (if needed)

1. Remove the oxygen sensors:

   • Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
   • Use an O2 sensor socket to carefully unscrew and remove the sensors from their respective locations.

2. Install new oxygen sensors:

   • Apply anti-seize compound to the threads of the new sensors.
   • Install the new sensors by hand to avoid cross-threading, then tighten to the manufacturer's torque specification (typically around 30 lb-ft).

3. Inspect and Replace Catalytic Converter (if necessary)

1. Remove the catalytic converter:

   • Disconnect the exhaust pipes from both ends of the catalytic converter. This may require cutting or unbolting clamps.
   • Remove any mounting brackets securing the converter.

2. Install the new catalytic converter:

   • Position the new catalytic converter in place, ensuring proper alignment with the exhaust system.
   • Secure the converter using the original or new gaskets and bolts, tightening to the specified torque (usually around 30-40 lb-ft).

4. Reconnect Battery and Clear Codes

• Reconnect the battery terminals securely.
• Use the OBD-II scanner to clear the P0420 code and any other stored codes.

5. Test Drive

• Start the engine and let it idle for a few minutes.
• Take the vehicle for a test drive to allow the PCM to re-evaluate the emissions system.