The Car Access System (CAS) authorizes the key and grants permission for ignition. Until the key is confirmed, starting is impossible: the starter motor receives no signal, and the anti-theft system stays active. Below: the failure symptoms, the check sequence, and the rules for replacing the module.
How CAS Works
CAS (Car Access System; German: Schlüssel- und Zündfreigabe) is the central unit for access and starting. The module authorizes the key and grants permission for ignition. Until authorization succeeds, the starting circuit stays inhibited.
Hence the three typical failure presentations: the message “Schlüssel nicht erkannt” (key not recognized), no signal to the starter motor (Anlassersignal), and an active anti-theft system (Wegfahrsperre).
In hardware, the system exists in four versions: CAS2, CAS3, CAS3+, CAS4. All four perform one function—key authorization and ignition release. The differences between the revisions are not covered in the source data.
Symptoms
- The engine does not start; there is no signal to the starter motor.
- The key is recognized only intermittently (sporadisch).
- The anti-theft system is active (Wegfahrsperre).
- Fault codes 9C55 and 9C56 sit in the CAS memory.
- Often alongside: the engine fires up and immediately stalls.
That last item isn’t a direct CAS symptom, but it does show up together with a failed module—an observation from related materials, not a CAS diagnostic indicator.
Causes
There are three causes, and they differ in likelihood and in the cost of checking them:
- the CAS module itself is faulty (CAS-Modul defekt);
- the remote control antenna in the steering column lock is faulty (Fernbedienungsantenne im Lenkschloss);
- the key battery is dead or the key is faulty (Schlüssel entladen/defekt).
The order of the list reflects check logic, not frequency: start with the cheapest and most accessible component—the key—then the antenna, and only then suspect the module.
Diagnosis
- Read CAS fault codes with ISTA (CAS-Fehlerauslesen).
- Test starting with the second key (Zweit-Schlüssel testen).
- Measure the antenna resistance (Antennen-Widerstand messen).
Service pointer: with communication and key recognition faults, the CAS / FEM / BDC modules get checked—they handle access, key recognition, and permission to start.
Step-by-Step Check
- Check the key battery and replace it if necessary.
- Check the antenna ring on the steering column lock.
- If the CAS is replaced, perform the mileage matching (Kilometer-Angleich)—this step is critical; without it, the car won’t move.
Vehicle identification uses the 17-character VIN (17-stellige VIN).
Repair
- Antenna ring—replacement.
- CAS module—replacement only with VIN programming (VIN-Programmierung).
Prevention
- Replace the key battery regularly.
Approximate Costs
| Item (per source) | Cost |
|---|---|
| Antenna ring (Antennenring) | negligible cost |
| CAS3+ repair (Instandsetzung) | moderate cost |
| New CAS + adaptation | significant cost |
The first item in the source cost list appears as “Position: Rahmen”—an unfilled template with no connection to CAS. What stood behind it cannot be reconstructed from the available data.
Caveats About the Source Data
The material this page is built on was assembled by an automatic linking system. Some of the links have nothing to do with CAS and should be read as separate topics, not as a continuation of the diagnosis.
The interlinking block picked up the codes 2A82 (intake VANOS), 2A87 (exhaust VANOS), 2AAF (exhaust VANOS, bank 2), 29CD (misfires), and 2B00 (fuel injector, cylinder 1), plus the N54 and S58 engine profiles and topics on the DPF, NOx (SCR/AdBlue), the climate control system, and the windshield wipers. None of them relate to the access system.
Also flagged: the BMW 1 Series F40, BMW 4 Series G26 Gran Coupé, and BMW 6 Series G32 Gran Turismo—they appear only as automatic links.
Source duplicates have been merged: the answer about CAS replacement was given twice, the “CAS / FEM / BDC prüfen” link and the “Fehlercode E714” article each repeated in two blocks, and so did the “engine fires and stalls” symptom. The statement about VIN privacy was duplicated in the input block.
| Code | Relation to the topic |
|---|---|
| 9C55 | CAS fault (symptoms) |
| 9C56 | CAS fault (symptoms) |
| E714 | CAS anti-theft function (Wegfahrsperre) |
| 2A82 | intake VANOS—not related to CAS |
| 2A87 | exhaust VANOS—not related to CAS |
| 2AAF | exhaust VANOS, bank 2—not related to CAS |
| 29CD | misfires—not related to CAS |
| 2B00 | fuel injector, cylinder 1—not related to CAS |
FAQ
Can you replace the CAS yourself?
No. It takes a specialized repair service (Instandsetzer) that transfers the VIN and the mileage (km). A swap without transferring the VIN and the mileage means the engine won’t start.
What happens to the VIN during the diagnostic lookup?
The VIN is processed entirely locally in the browser: it is neither stored nor passed to third parties.
The Bottom Line
When key recognition fails, the engine doesn’t start because the starting circuit is locked out—not because the starter motor or the fuel system failed. Start with the key battery and the second key, then measure the antenna resistance, and only after that consider replacing the CAS module.