How do you reset immobilizer 406 diesel?

To reset the immobilizer on a Peugeot 406 diesel, you typically need to use the vehicle's key. Insert the key into the ignition and turn it to the "On" position without starting the engine, then leave it for about 10 minutes. After that, turn the key off and try starting the engine. If the immobilizer still doesn’t reset, you may need to consult a professional or use diagnostic tools to reprogram the key or immobilizer system.