767 at purple promise, ahm is the "real time" boeing aircraft health monitoring system. There are no flight deck effects for this sensor, it just senses the bleed pressure after the pressure regulating valve but before the prsov. It will show -7 psi just about every single leg, with occasional psi spikes. Even with multiple sensors replaced it will still show -7 psi but the cockpit duct pressure uses the same 28vdc, I am just not sure if it is getting to this particular sensor.