Inmovilizador defectuoso

The security system that authorises the engine to run, faulty so that a legitimate key is refused or authorisation cannot be confirmed. It is deliberately built to fail closed — an immobiliser that let the engine run when unsure would not be one — so the outcome is always a non-starting vehicle rather than a degraded one.

The commonest faults are at the ends, not in the module. A transponder in the key that has failed, an antenna ring around the ignition barrel that has broken or come unplugged, or a key that has physically worn are all far more likely than the control unit. Trying a second key is the fastest test available and separates key from vehicle in seconds.

Module replacement is the case that needs care. These components are cryptographically paired, so a replacement engine or body module must be programmed to the vehicle before it will authorise anything — and on many manufacturers that requires dealer-level access and proof of ownership. Establish that a module can be paired before it is bought, since a used one from another vehicle may never authorise on this one and is then worthless.