what does it mean if my Ram 1500 DT (2019-Present) has a check engine light with code P0420?

Solution

1. Preparation

• Gather tools and components before beginning the repair.
• Disconnect the battery to ensure safety while working on the electrical system.

2. Inspect and Test Oxygen Sensors

1. Remove the upstream (pre-catalytic) oxygen sensor using an O2 sensor socket.
2. Inspect the sensor for damage or contamination.
3. Test the sensor’s resistance with a multimeter; replace if readings are outside manufacturer specifications.
4. Repeat the process for the downstream (post-catalytic) oxygen sensor.

3. Check Catalytic Converter

1. Inspect the catalytic converter for physical damage or signs of overheating (discoloration, dents).
2. If the converter is suspected to be faulty, perform a backpressure test using a backpressure gauge.
3. If backpressure exceeds specifications, replace the catalytic converter.

4. Replace Components (if necessary)

1. If either oxygen sensor or the catalytic converter needs replacement, install the new part in reverse order of removal.
2. Ensure all O2 sensor connections are secure and properly torqued to manufacturer specifications.
3. Reconnect the battery.