what does code P0420 mean for my GMC Sierra T1XX (2019-Present)

• •Check engine light illuminated
• •Decreased fuel efficiency
• •Loss of acceleration or power
• •Unusual exhaust smells (e.g., sulfur or rotten egg odor)
• •Rough idle or engine stalling
• •Increased emissions

1. 1Scan the vehicle's OBD-II system to confirm the P0420 code and check for any additional codes.
2. 2Inspect the exhaust system for any visible leaks, particularly around the catalytic converter and exhaust manifolds.
3. 3Check the condition of the oxygen sensors, especially the pre-catalytic and post-catalytic sensors.
4. 4Measure the voltage output of the oxygen sensors using a multimeter while the engine is running.
5. 5Test the catalytic converter temperature difference between the inlet and outlet using an infrared thermometer.
6. 6Inspect for any modifications or aftermarket parts that may affect exhaust flow or sensor readings.

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
• •O2 sensor socket
• •Multimeter
• •Socket set
• •Torque wrench
• •Infrared thermometer
• •Cutting tool

• •Oxygen sensors (if faulty)
• •Catalytic converter (if faulty)
• •Gaskets and seals for exhaust components