Final answer:
The cause of the tandem rear axle air suspension ride height rising above normal when the vehicle is unloaded could be a kinked air spring (bag) supply line, a leaking height control valve, or a leaking pressure protection valve.
Step-by-step explanation:
The cause of the tandem rear axle air suspension ride height rising above normal when the vehicle is unloaded could be a kinked air spring (bag) supply line, a leaking height control valve, or a leaking pressure protection valve.
A kinked air spring supply line can restrict the flow of air, causing the suspension ride height to rise. A leaking height control valve can allow air to escape, resulting in a higher ride height. Similarly, a leaking pressure protection valve can lead to air loss and higher ride height.
To determine the exact cause, a thorough inspection of the suspension system should be conducted by a qualified mechanic.