The TARDIS is heavily motivated to adhere to a strict set of moral rules. This might be due to programming, the influence of a long time relationship with a single Time Lord operator, or because it picked up the cultural mores of a civilization it had spent a long time with as part of an anthropological mission. Whatever the reason, it not only follows the code but also tries to force its operator and passengers to do so as well.
The TARDIS will have a strict code of behaviour. This could be an adoption of an existing code, like Bushido or the Ten Commandments, or a new set of rules agreed upon by the players and GM.
The TARDIS will never allow itself to break those rules and will also try to prevent any of its occupants from doing so either by shutting down critical systems, locking doors, freezing controls or possibly even taking off on its own, as it refuses to take part in such a violation of its principles. If the characters manage to force it to do so anyway, all further TARDIS Operation rolls will be at a +3 Difficulty for the rest of the adventure due to its sentience retreating inwards to avoid conscious participation.
This Trait raises the TARDIS’ Story Points by 2.