Copied from another post i made to another topic.
This is why 144 can't operate on its own and has to be dragged everywhere when not on depot.
221144 as a two car set cannot work on its own or used to strengthen another set.
It has a very noisy compressor rigged up in the luggage compartment.
If it could move on its own it would not tilt, the master tilt computer is on the 608 vehicle which is not present.
Whether or not tilt is operative on a 221 the hydraulic tilt system still has to be pressurized, controlled by the master tilt computer, if it's not then the vehicles can go off center (out of guage) causing a center detect fault. If you get one of them then it's out of service at a maximum of 40 mph which causes chaos on a 125 mph railway.
The only way i can think of to circumvent the above would be to do what cross country have done to their 221s and fit a steal bar to ensure the vehicle stays upright then the tilt system which is no longer required can be permanently isolated, the system would be de-pressurized and a center detect fault would never happen.
That's my view as a driver, if anybody can elaborate or correct me please feel free.