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

• •Check engine light illuminated
• •Decreased engine performance
• •Poor fuel economy
• •Engine misfires
• •Unusual exhaust smells (sulfur or rotten egg odor)
• •Increased emissions

1. 1Scan for error codes using an OBD-II scanner to confirm the P0420 code and check for any additional codes.
2. 2Inspect the exhaust system for any visible leaks or damage.
3. 3Use a multimeter to test the voltage output of the upstream and downstream oxygen sensors.
4. 4Measure the temperature difference between the inlet and outlet of the catalytic converter using a temperature gauge.
5. 5Check for any exhaust restrictions or blockages.
6. 6Verify that the engine is running at optimal conditions (fuel pressure, air intake, etc.).

After completing the repair, verify that the issue has been resolved:

• ✓Test the affected component to ensure it functions correctly
• ✓Check for any error codes or warning lights
• ✓Monitor the vehicle for a few days to ensure the issue does not recur

To prevent this issue from occurring again:

• •Follow the manufacturer's recommended maintenance schedule
• •Address warning signs early before they develop into major issues
• •Use quality parts and fluids recommended for your vehicle
• •Keep detailed records of all repairs and maintenance

• •OBD-II scanner
• •Multimeter
• •Temperature gauge
• •Socket set
• •Torque wrench

• •Upstream oxygen sensor
• •Downstream oxygen sensor
• •Catalytic converter (if necessary)