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

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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the vehicle's battery to ensure safety during repairs.
• Raise the vehicle using a jack and secure it with jack stands.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench, penetrating oil.
• Remove the upstream oxygen sensor using the O2 sensor socket.
• Inspect the sensor for contamination or damage.
• If faulty, replace it with a new sensor, ensuring it is properly torqued to manufacturer specifications (typically around 30 ft-lbs).
• Repeat the process for the downstream oxygen sensor if required.

3. Inspect and Replace the Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if necessary).
• Remove any heat shields covering the catalytic converter.
• Disconnect the exhaust pipes from the catalytic converter using the socket set.
• Inspect the catalytic converter for signs of clogging or damage.
• If replacement is necessary, install the new catalytic converter, ensuring all bolts are torqued to manufacturer specifications.
• Reattach any heat shields.

4. Address Exhaust Leaks

• Inspect all exhaust joints and gaskets for leaks.
• Replace any damaged gaskets or seals.
• Use exhaust sealant if necessary to ensure a proper seal.

5. Reset the Check Engine Light

• Reconnect the vehicle's battery.
• Use an OBD-II scanner to clear the P0420 code.
• Perform a test drive to monitor for any reoccurrence of the check engine light.