BMW CAS Module Failure Symptoms – Here’s What May Go Wrong

In the last few decades, cars started to have more and more options, most of which are controlled electronically. No matter what make and model you choose these days, it will almost certainly be packed full of all sorts of electronics. Having so many different options will almost certainly require these modules for them to work properly, which is why you cannot really get rid of them.

CAS problems highlights

• Module's importance:High
• Prone to failure:Yes
• Reasons for failure:Age, connection, physical damage
• Ways to reset:Noway to reset
• Sphere of control:Verifying the proper key
• Symptoms of failing:No start
• Price to repair:Repair is impossible
• Price to replace:$800 - $1,200

What is a CAS module in a BMW?

Before talking about how this module fails, we believe that it's important for you to understand what it does. CAS stands for Car Access System and it has a few different uses, but the two most important ones are to monitor the vehicle's anti-theft alarm system and to allow the vehicle to start.

This module generates a random code for the key every single time the vehicle is started, which synchronizes with the vehicle's ECU (Engine Control Unit). You should also know that BMW likes to call their ECUs DME (gasoline-powered vehicles) or DDE (diesel-powered vehicles).

Basically, for the vehicle to start, the key, the CAS, and the ECU all need to be synchronized, otherwise starting the engine simply will not be possible. The CAS module also contains important information about the vehicle, such as the VIN (Vehicle Identification Number), type of engine, transmission, options, and so on.

Now that you understand what this module's purpose is, let's talk a little bit about why it fails.

Why does the CAS module fail?

• Water intrusion

As you may know, electronics don't like water and the CAS module on BMWs is no exception. If water makes its way into the CAS, it will almost certainly damage it and you will find that your car will start acting up.

• Physical damage

Maybe you've decided to remove the CAS module and, by mistake, you've dropped it on the ground or you've hit it accidentally. Even though the Germans are known for their cars' robust build quality, these modules simply aren't bulletproof. Any sort of physical damage can make it go bad, which is why it is to be avoided at all costs.

• Normal wear because of age and usage

Maybe your BMW is a little bit older and, as you probably already know, things will start to go bad one by one after some time and this module, among others, is no exception.

How to tell if there's a problem with the CAS?

Before rushing to conclusions about what exactly is wrong with your BMW, we believe that it's important for you to know about some of the possible symptoms of a defective CAS module. Here are some of them:

1) Error message on the iDrive screen

Did you notice a warning message on the iDrive screen? It might have been because of a CAS fault. Sometimes, it might tell you only that there's an electrical fault, but this should be enough for you to do some troubleshooting.

2) Vehicle doesn't crank

You push the start button, yet nothing happens. You are absolutely sure that the battery is good and the key fob isn't faulty. Well, in this case, you might want to start thinking about checking that CAS module we keep mentioning.

3) Vehicle doesn't accept key

If your BMW tells you that the key you've been using for the last few years is no longer good, you might want to consider checking the CAS module. Surely nobody messed with your car's key, right?

4) The car cranks, but doesn't start

If you push the start button and the car cranks, but it doesn't start, it might first seem to you like there's a problem somewhere else, such as with the fuel pump. If you think about it, you are not far from the truth, since, much like in the case of an immobilizer, if the module doesn't recognize the key, it will not send any power to the fuel pump, which is why your car won't start.

5) The vehicle may start, but it stalls immediately

This might seem very strange, but in certain cases, the car might actually start for a brief moment and then immediately shut off. Again, this might seem like an engine or fuel pump-related problem, but it might actually be because of a CAS module that's acting up.

6) Steering lock warning light in the instrument cluster

Have you noticed the yellow warning light resembling the steering wheel? If you're unfamiliar with it, you should know that this warning light appears whenever there's a problem with the electronic steering column lock, which is also controlled by the CAS module on BMWs. Also, you should know that this warning light can be observed in cars manufactured by other makers and it is not a warning light specific to BMW.

How to fix the problems?

Fixing this problem should ideally start with performing a diagnostic. This is one of the most helpful tools when dealing with issues such as this one since there isn't much else that you can do to make your life a little bit easier. The diagnostic tool will tell you whether there's a problem with the module itself or if the key fob and the CAS are desynchronized.

Sometimes, the problems can be fixed simply by resetting this module to factory settings, especially if we're talking about mismatched keys. However, if you find that you simply cannot communicate with the CAS through the diagnostic tool, the problem might be somewhere else, to be precise, in the module itself.

If you want to check it for water intrusion or physical damage, you should know that this module is located under the steering column. To get to it, you simply have to remove the plastic cover that protects the steering column, which is above the pedals, and then you will notice the module. If you have trouble locating it, you should know that it looks like a black or white box. When doing this, we would recommend you to be very careful when removing it and especially when disconnecting it and to also check for a diagram before doing anything.

Problems related to any sort of electronic module should really be dealt with only by people that actually know what they are doing and who have the right tools for the job. If you are an amateur, or if you simply aren't sure of what you're doing, we would recommend you ask a specialist for help.

They have probably dealt with this kind of issue before and they will have your car working in no time. Labor might not be exactly cheap in certain situations, but it's way better than damaging what might have been a good working module.

If the CAS is completely gone, it would be best to replace it with a brand-new one from the dealer and avoid any sort of repair, especially if you don't know too much about how it works. A brand-new CAS can be quite expensive, which is why you might think about trying to buy a used part.

We would only recommend you to do so if you can buy one that is verified and if the price difference is big enough. Also, regardless of whether this module is new or used, it will still need coding, so keep this in mind as well.

How to avoid issues in the future?

Apart from cleaning the drains from time to time and checking that all the seals are sealing properly, there really isn't much you can do to prevent such issues. This module is hidden quite well, which is why it's quite rare for drivers to damage them.

Should you drive like this?

To put it short, no. You can never be sure when the car will simply not want to start anymore and you might find yourself stranded very far away from home. We would recommend you have this problem checked by a specialist as soon as possible to avoid such unpleasant situations.

Final thoughts

Electronic modules these days control pretty much anything in a car and if one were to fail, it will almost certainly cause all sorts of issues. As much as these modern options can make the driver's life easier, they can also become quite a bit of a nightmare when they go wrong.