Where is the engine imobilizer

The "immobilizer" is an electrical device that relies on the use of an appropriately programmed key to start the vehicle. You cannot repair or diagnose this unless you have a proper diagnostic test or programming procedure performed on new keys. If you are not using the same keys as you were before the problem occurred, this can be your problem. If the keys are the same, I doubt it's an immobilizer problem. Either way, testing by a professional, experienced technician using proper test equipment and reference materials is needed -- whether it be immobilizer related concerns, ignition spark concern, fuel delivery concern, engine compression concern, engine timing concern or an air intake concern. Good luck.