BMW catalyst monitor not ready.

BMW Catalyst Monitor Not Ready: What Should I Do?

Is the catalyst monitor not ready on your BMW car? That should not worry you. You only need to perform a catalytic converter drive cycle to make it ready.

Your BMW car is a complex machine with many monitors that track system functions. They can be either continuous or non-continuous monitors. The catalyst monitor is an example of a non-continuous monitor that works when the engine runs at a certain speed. 

This article focuses on the cause of the catalyst monitor in unready status and how to change it. Let’s dive in!

BMW catalyst monitor not ready.
BMW catalyst monitor not ready.

What Is The Catalyst Monitor On BMW Used For?

To understand what a catalyst monitor on BMW does, we should first know what a catalyst converter does. A catalysts converter helps reduce air pollutants from the exhaust into less harmful forms before they get into the air, which maintains the health and overall performance of your car.

A catalyst monitor on BMW or any other car determines if the catalytic converter is working correctly. It does that by monitoring the oxygen levels entering and leaving the converter unit, which means oxygen sensors are crucial in this process.

By comparing the data from upstream and downstream oxygen sensors, a catalyst monitor can determine the efficiency of a catalytic converter. Under normal working conditions, the catalyst converter should use almost all oxygen in the incoming air.

The efficiency of the catalytic converter should not be below 50% for two consecutive drive cycles. If that happens, Power Control Module (PCM) stores the code. That makes the CHECK ENGINE light come on.

Why Is The BMW Catalyst Monitor Not Ready?

The output of the catalyst monitor can be ready or not ready. If the status indicates the latter, a requisite drive cycle has not run. That occurs due to your driving habits.

The catalyst monitor requires certain conditions to run successfully. These are usually the speed, throttle position, and combination of the two. If you only drive in the busy city streets and never get to highway speeds, your catalysts monitor may never run.

The speed and duration required to trigger the catalyst monitor into action may depend on the car brand and model.

What Should I Do When The Catalyst Monitor Is Not Ready?

You should follow the steps below when your BMW catalyst monitor is not ready.
You should follow the steps below when your BMW catalyst monitor is not ready.

You can change your BMW catalyst monitor not ready status by doing routine checks and procedures yourself. Sometimes you may need help from your mechanic.

If your catalyst monitor shows not ready, resolve it by doing the following:

Check Engine Light

This is the first step if your BMW catalyst monitor is not ready. As already mentioned, PCM will store a pending code if the catalytic converter is faulty or its efficiency drops to below 50%. The catalyst monitor will not run if there is an active trouble code.

If the check engine light is on, it may be the culprit. Get an OBD2 scanner to read the DTC and fix the problem. But if it is off, continue to the next check.

Check Coolant Temperature

If your BMW catalyst monitor is not ready, it may be due to the high coolant temperature. The drive cycle begins when the engine temperature is between 11F-122F. If that is not the case, let the engine cool down, probably overnight.

Make sure to check if there is any coolant leak because it can also cause the coolant temperature goes up. Fix the problem as soon as possible.

Perform Drive Cycle

If none of the above is the case, you need to perform a catalytic converter drive cycle. Its objective is to bring the engine coolant to the correct temperature and make the exhaust hot enough to burn soot that may be clogging it.

  • Start your engine and turn on the AC and rear defroster. Leave them running for two minutes.
  • Switch off AC and rear defroster and accelerate to 55 MPH.
  • Drive at this speed for about 3 minutes. That allows the ECU to conduct self-tests on EVAP Purge Flow, Misfire Detection, oxygen sensor response, Fuel Trim, and Air Intrusive System (AIS).
  • Decelerate to 20 MPH without shifting gears or stepping on the brake pedal. Once again, the ECU performs self-tests on Long Term Fuel Trims, EGR System, and EVAP Purge System.
  • Accelerate again at ¾ throttle to 55 MPH and maintain that speed for another five minutes. That allows the tests performed during the first acceleration to repeat.
  • Decelerate and bring your car to a stop. Again, ECU performs the same tests it did during the first deceleration. This process may take up to 5 complete driving cycles for the verdict to come out, especially with an unconnected battery terminal or marginal catalytic converter.
  • Let the engine idle for another 2 minutes. All monitors should be ready now, including the catalyst monitor. If that does not happen, there is probably a problem in the system that requires further diagnosis.

For that, you may need the help of a mechanic or use an OBD2 scanner if you are a DIYer to read any pending and active DTCs. You can then decide on what to do next after that.  

How Long Does It Take For The BMW Catalyst Monitor To Be Ready?

The time it will take for the catalyst monitor to get ready depends on the status of other monitors. A catalytic converter drive cycle typically takes about 10-15 minutes. But that assumes the system is not performing a test check on other system monitors, such as EVAP and EGR monitors. It may take a bit longer if that is not the case.

Also, the drive cycle to get the catalyst monitor ready can be specific to your BMW model. Refer to the manual to do it according to the manufacturer’s specification.


BMW catalyst monitor not ready is not a common occurrence, especially if you drive at highway speeds most of the time. There is no need to panic if you see it. You probably only need to perform a catalytic converter drive cycle described in this article. If that does not help, use an OBD2 scanner or call your mechanic for assistance.

Leave a Comment

Your email address will not be published. Required fields are marked *