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

Learn how to diagnose and fix P0420 catalytic converter efficiency issue in GMC Sierra T1XX. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, jack and jack stands, safety glasses, gloves.
• Safety Warnings: Disconnect the battery before working on electrical systems. Allow the engine and exhaust system to cool before starting work.

2. Inspect and Repair Exhaust Leaks

1. Raise the vehicle using a jack and secure it with jack stands.
2. Visually inspect the entire exhaust system from the engine to the tailpipe for any signs of leaks or damage.
3. If leaks are found, replace any damaged gaskets or components using appropriate replacement parts.

3. Test and Replace Oxygen Sensors (if faulty)

1. Locate the upstream and downstream oxygen sensors on the exhaust system.
2. Disconnect the electrical connectors from each sensor.
3. Use a multimeter to test the voltage output of each sensor. Upstream should fluctuate between 0.1V and 0.9V; downstream should be relatively stable.
4. If either sensor is faulty, remove it using a socket wrench and replace with a new sensor, ensuring the threads are clean.
5. Reconnect electrical connectors and ensure they are secure.

4. Catalytic Converter Inspection

1. Inspect the catalytic converter for physical damage or blockage.
2. If there are signs of damage or if the temperature difference before and after the catalytic converter is not within specifications, replace the catalytic converter.
3. Ensure all connections to the catalytic converter are tight and use new gaskets if necessary.

5. Clear Codes and Test Drive

1. Reconnect the battery and use the OBD-II scanner to clear the P0420 code.
2. Take the vehicle for a test drive to ensure it operates normally and monitor for any check engine light reactivation.