Check Engine Light P0420 on 2020 Aviator - Catalyst Efficiency?

Hello Chris,

The P0420 code on your 2020 Lincoln Aviator Reserve indicates that the catalytic converter on Bank 1 is not operating at optimal efficiency. While it often points to the catalytic converter itself, there are several other potential causes that should be investigated first.

Here are the common causes and diagnostic steps:

1. Oxygen Sensor Malfunction: The most common culprit after the catalytic converter itself. The post-catalytic converter (downstream) oxygen sensor monitors the converter's efficiency. If this sensor is faulty, it might incorrectly report low efficiency. A pre-catalytic converter (upstream) O2 sensor issue can also cause the converter to fail prematurely due to incorrect fuel mixture.
2. Exhaust Leaks: Any leak in the exhaust system before or near the catalytic converter can allow unmetered air in, tricking the O2 sensors and causing a P0420 code. Listen for hissing sounds, especially when the engine is cold.
3. Engine Misfires or Fuel System Issues: Persistent engine misfires (P030x codes) or issues with fuel injectors can send unburnt fuel into the catalytic converter, causing it to overheat and fail over time. Check for any other pending or stored codes.
4. Catalytic Converter Failure: Over time, catalytic converters can degrade due to age, contamination, or damage from other engine problems. This is often the most expensive fix.

What you can do:

• Check for Exhaust Leaks: Visually inspect the exhaust system for cracks, rust, or loose connections, especially around the manifold and catalytic converter.
• Monitor O2 Sensor Data: If your scan tool has live data capabilities, monitor the readings from both upstream and downstream O2 sensors on Bank 1. The downstream sensor's voltage should be relatively stable compared to the fluctuating upstream sensor if the converter is working correctly.
• Check for Other Codes: Ensure there are no other active or pending codes that might point to a root cause like misfires or fuel trim issues.

When to see a shop:

If you've checked for exhaust leaks and the O2 sensor data doesn't clearly point to a faulty sensor, it's best to take your Aviator to a qualified technician. They can perform more advanced diagnostics, such as:

• Backpressure Test: To determine if the catalytic converter is clogged.
• Smoke Test: To precisely locate any exhaust leaks.
• Detailed O2 Sensor Analysis: Using professional diagnostic equipment to confirm sensor operation.

Ignoring a P0420 code can lead to reduced fuel economy, increased emissions, and potentially more costly repairs down the line if the underlying issue is not addressed.