BMW's CAS (Car Access System) is the heart of every modern BMW immobiliser — and one of its weakest links. CAS2, CAS3, CAS3+ and CAS4 all have well-known failure modes.
Symptoms
Cranks but no start, key not recognised, EWS lockout, steering lock active, intermittent no-start that comes and goes.
Common cause — water ingress
CAS modules sit in the driver's footwell. A blocked bulkhead drain or windscreen leak destroys CAS units regularly on E60, E90, E70, F10 and F30.
Common cause — EEPROM corruption
ISN, VIN and key data live in the CAS EEPROM. Voltage spikes (jump-starts, flat battery) corrupt it — symptoms include random no-start and 'key not recognised'.
How we fix it mobile
EEPROM read, repair and rewrite — or supply, code and program a replacement CAS unit with your existing keys synced. Saves a £900+ dealer bill.
Related services on StageMyCar: BMW CAS key programming and BMW auto locksmith in Harrow.