Why Is BMW Catalytic Converter Not Ready? [With Solutions]

Have you been handed the P420, P0420, or P430 codes from your BMW PCM? These errors appears when the BMW catalytic converter is not ready. 

The catalytic converter helps break down the car’s harmful pollutants using oxygen. And the monitor ensures whether the converter is actively working or not.

But there are times when the catalytic converter might not trigger or have error messages like ‘not ready. Here’s what you can do to solve them. 

Why is the BMW Catalytic Converter Monitor Not Ready? 

While digging about the BMW catalytic converter monitor, I found that a catalytic converter monitor isn’t something that you simply install and it starts working. Rather it’s a much more intricate process. The PCM controls it, and several aspects are key to triggering the catalytic monitor. Without them, the monitor would constantly read ‘not ready. 

Loose Cell Sensors 

The first issue to note is the disconnected or loose cell sensors. If your cell sensor is loose or disconnected, it will invariably reset the memory of the PCM. Needless to say, the catalytic monitor gets triggered by the metrics shown by the PCM; without the cell sensor data, the PCM will not trigger the catalytic monitor. 

Removing the Stored Codes 

The fault codes are five-digit troubleshooting codes that are stored in the PCM. This helps to identify a specific type of problem and trigger the relevant monitor for it. An OBDII scanner can monitor the codes themselves. 

This specific scanner can also be used to remove the codes. Once the code is removed, the PCM data needs to count from zero again to be able to trigger any kind of monitoring in the car. 

Performance Tuners 

Performance tuners are installed in the car to increase or boost the performance of the car. Though I have never tried tuning, I know that tuning requires changing the car’s internal programming. And any change in the internal programming structure can completely alter the monitoring ability of the car. 

Using a Simulator 

I already mentioned how you need to achieve certain drive metrics to trigger the PCM and the converter monitor. Many people go for a shortcut in using a simulator to trigger the monitor. 

If the PCM can detect any kind of misleading change in the data, it will automatically shut down all the monitors, including the converter one.

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What to Do if the BMW Catalytic Monitor is Not Ready? 

The catalytic monitor will show either ready or not ready, depending on the state of the converter. I’ve found that most of the time, it will not show ‘not ready’ because the converter has not reached the required drive cycle to be able to start monitoring. Here’s how to get over the issues. 

Turn off the Engine Lights 

The first thing to do is resolve any kind of active fault codes on the engine. The manual says that the converter monitor might not kick in if there are any active fault codes. 

Ensure Coolant Temperature 

One of the key points for starting a catalytic converter monitor is that the engine needs to be cold. For BMW, this range generally falls between 6 degrees Celcius and 50 degrees Celcius. Make sure the engine gets a cold start for the monitoring to be ready. 

Keep Idle Running 

If you are from a cold region like I am, the engine needs to catch up to the optimum temperature level. I suggest you fire up the engine and let it rest for about 2 minutes before going. 

Run at 55 mph 

This is the start of a series of steps that you will need to do in succession. First, get your car up to 55 mph and keep it steady there. do not use cruise control. The constant speed will trigger the fuel monitor. 

Decelerate to 20 mph

Now bring the car down to 20 mph. keep the car steady at this speed. It will take the lower count reading for the drive cycle. 

Accelerate Again 

With both the higher and lower count on board, the converter monitor can then run the diagnostics. 

Bring your car to a halt and use an OBDII meter to check whether the CCM is ready or not. Ideally, it should start working. 

But what if it doesn’t? That indicates a faulty catalytic converter monitor.

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What are the Signs of a Bad Catalytic Converter?

Like most other car parts, there are almost always telltale signs that your car has a bad catalytic converter. 

Note that there can be two reasons behind the catalytic converter not being ready – a faulty catalytic converter or a detection issue. 

Here are some common signs that I realized were present in my car all along. 

Engine Misfiring 

This is a common issue that is also often attributed to other component failures. What you can do is check whether the oil has entered the converter or if the converter has heated up excessively while firing up the car.

Power Loss 

The drivetrain will lose power when you either go up or down a slope. This occurs due to the clogged catalytic converter. The clogging can be either full or partial. 

Performance Reduction 

The engine cannot perform at its optimum level with converter issues. Pressure often builds up at the back of the converter, which, in turn, reduces the engine output. 

Fuel Vapor 

An issue with the catalytic converter will also affect the car’s fuel. I ran a fuel vapor test on my car to test for the issue. All I had to do was rev the engine after removing the cover of the carburetor on my car. 

A cloud of fuel vapor was visible, which suggests that the catalytic converter might be clogged. 

Increased Emission 

The last telltale sign of a failing catalytic converter is the exact thing it’s supposed to control, the emission. If you notice somewhat increased emission from the back exhaust, chances are the catalytic converter is clogged.

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Frequently Asked Questions 

Now let’s look at some frequently asked questions regarding the BMW catalytic converter monitor. 

Is A Catalytic Converter Monitor Expensive? 

Catalytic converter monitors are part of the converter itself. And yes, they are fairly expensive at over $1000 each. Depending on the engine type, some cars might even have more than one converter. 

How Does A Drive Cycle Complete In A BMW?

The process of the drive cycle is almost as standard as other cars. You can check points three through six above to get an idea about the drive cycle completion. 

Is It Possible To Pass Emissions Without Catalytic Not Being Ready? 

It will depend on your car. Almost every new model requires CCM. But depending on some older models, it might be allowed to pass without being completely ready. 

How Long Do I Have To Drive For A Complete Cycle? 

It depends from car to car. Ideally, you will have to drive for about 20 minutes following all the steps for the cycle to complete. 


That wraps up my take on the Unready BMW catalytic converter monitor issue. While it’s not uncommon to see this problem, many people think it is an issue with the converter itself. I know because I did too. 

But that is seldom the case. Just make sure that you run the proper diagnostics to see whether it’s the actual converter that is the issue or the drive cycle that is incomplete. 

This simple trick will help you solve a lot of money and might not even require a visit to the dealership.

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