How to Fix Mini Cooper Engine Light and P0420 Error Code

by parker
YouTube video

Welcome back to another video from The Savage Garage. Today, we have a job on the Mini Cooper to fix the engine light issue. Initially, the car was running fine, but after a few weeks on the road, complaints started to arise about the engine light being constantly on, decreased fuel economy, and a sluggish and juddery feeling while driving. In this article, we will dive into the details of how to diagnose and fix this issue step-by-step.

Diagnosing the Issue

To diagnose the issue, we will be using a scan tool. The host of the video recommends the Topton scan tool, which provides generic codes and allows you to analyze data. The first step is to plug the scan tool into the Mini Cooper and check for any error codes. In this case, the scan tool reveals a P0420 error code, which indicates a catalyst system efficiency below the threshold in Bank 1. This code is commonly associated with catalytic converter malfunction in various car models.

Understanding the Catalytic Converter

The catalytic converter is responsible for reducing emissions by converting harmful gases into less harmful substances. In this Mini Cooper, the issue seems to be related to the catalytic converter not working properly. To confirm this, the host performs a live data analysis using the scan tool. The data shows that both oxygen sensors in Bank 1 are reading similar voltage levels, indicating that the catalytic converter is not burning off carbon dioxide (CO2) as it should be.

Possible Causes and Solutions

There could be several reasons why the catalytic converter is not functioning properly. In this particular case, the Mini Cooper had recently undergone a head gasket repair, which might have caused damage to the catalytic converter. However, it is difficult to determine the exact cause without further investigation. To fix the issue, the host plans to replace the catalytic converter, along with the two oxygen sensors attached to it.

Replacing the Catalytic Converter

The next step is to replace the faulty catalytic converter. The host shows the new catalytic converter, which includes the exhaust manifold, a flexi joint, and the two oxygen sensor ports. He also provides a quick overview of where the catalytic converter is located in the Mini Cooper’s engine bay.

To begin the replacement process, the host removes the coolant reservoir and the heat shield for better access to the manifold bolts. He then uses an electric ratchet to remove the manifold bolts. It is important to note that the specific number and size of bolts may vary depending on the car model.

Once the bolts are removed, the old catalytic converter can be detached from the exhaust manifold. Finally, the host demonstrates how to disconnect the oxygen sensor wiring, install the new catalytic converter, and reassemble the components.


In conclusion, a P0420 error code in a Mini Cooper indicates a catalytic converter issue. By using a scan tool for diagnosis and performing a live data analysis, the host identified that the catalytic converter was not operating properly. To fix the issue, he decided to replace the catalytic converter and the oxygen sensors associated with it. The replacement process involved removing the necessary components, including the coolant reservoir and the heat shield, to gain access to the manifold bolts. Once the new catalytic converter was installed, the host reassembled the components.

By following the step-by-step process described in this article, you can fix the engine light issue on your Mini Cooper and enhance its overall performance.

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