The P0420 diagnostic trouble code (DTC) is one of the most frequently encountered alerts that illuminates the Check Engine Light (CEL) on a modern vehicle. This code, which translates to “Catalyst System Efficiency Below Threshold (Bank 1),” signifies that the vehicle’s onboard computer, or Engine Control Unit (ECU), has detected the catalytic converter is not performing its emissions ...
Start by checking for any exhaust leaks or damage. Then, see if the oxygen sensors are working properly. If they are, you might need to replace a faulty catalytic converter. Taking care of the fuel system can also help. Want to handle these steps quickly and avoid future problems?
This excess fuel reduces catalytic converter effectiveness and can trigger code P0420. In such cases, replacing worn spark plugs (or ignition coils if needed) often solves the issue.
HowtoFixP0420 Engine Code 1. Check for a clogged catalytic converter. 2. Check for a bad oxygen sensor. 3. Check for a misfire. 4. Perform a smoke test. 5. Clear the code and retest.
Cause: Engine issues that lead to unburned fuel entering the exhaust can overheat and damage the catalytic converter, resulting in the P0420 code. Fix: Diagnose and repair the underlying engine issue, which may involve replacing spark plugs, fuel injectors, or addressing vacuum leaks.
When your downstream O2 sensor detects that the converter is not operating up to proper spec – it sends a warning. This warning comes in an engine trouble code – PO420 or PO421. Depending on the symptoms, there are a few likely causes and solutions.
In this guide we’ll break down what P0420 means, how to diagnose the underlying problem, and what steps you can take to fix it – whether you’re a DIYer or working with a shop.
When your downstream O2 sensor detects that the converter is not operating up to proper spec – it sends a warning. This warning comes in an engine trouble code – PO420 or PO421. Depending on the symptoms, there are a few likely causes and solutions.