Nissan P155b-00 [ RECOMMENDED ✠]
The code signals a stuck-closed coolant bypass valve. While it may seem minor, it carries the real risk of engine overheating and catastrophic damage. The good news: the repair is well-understood, parts are readily available, and a competent shop or DIYer can fix it in a few hours.
In modern Nissan automotive networks, codes within the typically govern manufacturer-controlled auxiliary systems. These often relate to electronic throttle control systems, boost pressure controls, or transmission-to-engine load signaling. nissan p155b-00