how to fix P0420 code on Ram 1500 DT (2019-Present)

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, jack and jack stands, backpressure gauge.
• Disconnect the battery to ensure safety while working on electrical components.
• Raise the vehicle using a jack and secure it with jack stands.

2. Inspect Exhaust System

• Sub-steps:
  • Visually inspect the entire exhaust system for cracks, holes, or loose connections.
  • Pay particular attention to the welds and joints.
  • Repair or replace any damaged exhaust components found during inspection.

3. Test Oxygen Sensors

• Sub-steps:
  • Remove the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  • Connect the multimeter to the sensor output and measure voltage while the engine runs.
  • Verify that the upstream sensor fluctuates between 0.1V and 0.9V and the downstream sensor remains relatively stable.
  • Replace any faulty oxygen sensors.

4. Check Catalytic Converter

• Sub-steps:
  • If the oxygen sensors are functioning correctly, check the catalytic converter for clogging.
  • Use a backpressure gauge to measure exhaust backpressure; it should be below 1.5 psi at idle.
  • If backpressure is high, the catalytic converter is likely clogged and should be replaced.

5. Replace Catalytic Converter (if necessary)

• Sub-steps:
  • Remove the old catalytic converter by unbolting it from the exhaust system.
  • Install the new catalytic converter, ensuring proper alignment with the exhaust pipes.
  • Torque the bolts to the manufacturer’s specifications (typically around 30-40 ft-lbs, but verify for your specific model).
  • Reinstall the oxygen sensors in the new catalytic converter.