[particlewave]

A honk means something is wrong.

Do you have a Bentley? It's a simple circuit, so testing a few test points would tell you what's going on.
Check for ground signal at the immobilizer for the lock and unlock wires when that circuit is activated to confirm that the drivers lock mechanism microswitches are working correctly. Then check to see that the passenger door interlocks are sending the correct ground signal to the immobilizer to let it know that it's ok to lock the passenger door and arm the alarm.

My guess is probably the "passenger door safe" microswitch, but testing will tell you for sure.