A working key provides a useful comparison when the spare will not start the vehicle. It does not prove which part of the second key or recognition process is responsible. Describe whether the spare unlocks doors, switches the ignition on or triggers a specific warning.
Bring the full key history
Tell the workshop whether the spare ever worked, when it was last used and whether it was newly supplied or repaired. Bring all available keys when requested and be prepared to establish ownership or authority for the work.
Do not dismantle security components or request an immobiliser bypass to avoid diagnosing the failed key. The specialist should check the supported recognition and programming route for the vehicle. Keep the working key safe and avoid experimental procedures that could affect it. An enquiry with vehicle details and the different responses of both keys is more useful than a generic request to replace the immobiliser module.
Related help
Browse all fault guides or use the vehicle module finder to prepare your enquiry. Include the vehicle, symptoms, complete fault codes and any previous test results. Assessment scope and compatibility must be confirmed before booking or sending a unit.