Audi S4 will not start for some time

The owner of this Audi S4 called dejectedly last week: from one moment to the next, his car would not start. In fact, the ignition wouldn't even turn on anymore. He took the car to a garage where they found out that the BCM2 module was not turning on the ignition. 

The BCM2 was replaced with a used one, but unfortunately the learning of this also failed. There a new key was bought from the dealer, but this also did not help. In the meantime 800 euros and 4 months later, the owner had had enough. After a few calls, the car car was picked up at the garage and the car came here for further investigation.
The BCM2 immobilizer system from Audi (WFS generation 5, used in A4, A6 and A8 from 2008-2017 and various Lamborghinis ) is a very complex system with many small snags (depending on type and year of manufacture and even in terms of software version, they are built differently).

Simple structure BCM2 immo system: In the BCM2, engine ECU, transmission, keys and the ELV (steering column lock, only until 2012) contain a unique CS code. If any of the components is replaced, the CS code no longer matches and the vehicle either does not turn on, or the ignition will does not turn on.

As a first step, the original “faulty” BCM was reinstalled, after which the key status was checked. This showed that the new key was pre-coded (dealer key), locked and programmed, but not authorized. The original key was no longer recognized by the system.

What does this tell us? A “dealer key,” as the name implies, comes from the dealer and is factory pre-coded with the correct CS code for this chassis number. Once the key is learned, it is locked and married to the vehicle. Yet this key did not give authorization, even though it was ordered by chassis number. So, clear story as to why the car will not turn on ignition NOW. But, is this now the original problem? Or was this problem created during diagnosis and do we have another problem? Unfortunately, I have learned over the years to not to cheer too early! It frequently happens that during the diagnostic process new problems are created that have nothing to do with the first fault. Think for example replacing certain parts that are not correct, or messing around in the coding /programming of the vehicle. Another common example is damaging connectors by measuring on them with incorrect measuring tools (clamping force connector pin is lost).
Anyway, to begin with, we make a new key. Making an after-market key is different than programming a key from the dealer. The after-market key is not pre-coded with the CS, we have to put it in manually. So first we have to make a dealer key first. Now how do we get that CS if we no longer have a working key?

In our case, we are dealing with a BCM2 with a production date AFTER 2013. From 2013 onwards these modules are more protected against reading the immodata, it is even in some cases, these modules are completely blocked during the attempt to extract the data!

With special equipment we can still get this data out (see photo). After precoding the key and then programming it, the vehicle struck without any problems.
So what was defective in the first place and where did it go wrong? The first thing to note is that this vehicle once had a new “immo set. That is meaning that all immo related components were completely transferred from a donor car. Then an imitation key was programmed. This was the only key the owner had. This key malfunctioned causing the ignition to no longer turn on. The garage replaced the BCM2 module (for nothing) and could not learn it. This learning did not work because the defective key was not recognized. Why didn't I learn the new ordered key?

This key was as said ordered at the dealer on chassis number and is thus pre-coded delivered with the CS for this Audi. But, since a new immo set came in at some point, this CS does not match with the CS programmed into the car, making this (expensive) key can be used.
With the aftermarket key it did work because we manually precoded it with the correct CS. All in all, the car was running again the same day.
Of course, the customer was immediately provided with a spare key, so that the next time he himself can take the first diagnostic step, namely by trying the spare key!