DTC C1A13-64: Pressure Does Not Decrease When Venting Gallery - Signal plausibility failure: Action

WARNING: This page is about a different car, the 2016 Land Rover LR4, 2015 Land Rover LR4, and 2014 Land Rover LR4. However, it is still accessible from the selected car via links, so may be relevant.

Using the manufacturer approved diagnostic system, test the operation of the exhaust valve (vehicle ride height interface)
Check the gallery pipe for blockages/damage/crushing
Check the air suspension exhaust silencer for blockages/restrictions