DTC C1803: Exhaust Solenoid: Description
WARNING: This page is about a different car, the 2013 Nissan Armada. However, it is still accessible from the selected car via links, so may be relevant.
The exhaust valve solenoid controls the vent function of the suspension control system. The exhaust valve solenoid is built into the suspension air compressor. The suspension control unit supplies voltage to the exhaust valve solenoid to activate it.