ASE A4 Suspension and SteeringSuspension System Diagnosis and RepairEasy
A vehicle equipped with an air suspension system exhibits a consistent sag on the right front corner after being parked overnight. When the engine is started, the air compressor runs for an extended period, and the right front corner eventually rises to the correct height. The system holds pressure normally throughout the day while driving. Which of the following is the MOST likely cause of this condition?
- AA clogged air dryer in the compressor assembly.
- BA faulty air suspension compressor.
- CA defective ride height sensor on the right front.
- DA leaking air spring (air bag) on the right front.
Show answer & explanationAnswer & explanation
Correct answer: D. A leaking air spring (air bag) on the right front.
A sag that develops overnight but can be reinflated suggests a slow leak in the air spring itself, allowing air to escape when the system is static.
Why the other options are wrong
- A. A clogged air dryer would affect the compressor's efficiency or introduce moisture into the system, but wouldn't directly cause a specific corner to sag overnight and then successfully reinflate.
- B. A faulty compressor would either not run, run but not build pressure, or be excessively noisy, but wouldn't typically cause a corner to sag overnight and then reinflate.
- C. A defective ride height sensor would likely cause incorrect height readings and potentially an always-low or always-high condition, or a DTC, not a slow overnight sag that corrects.
Air Spring Leak
An air spring (air bag) leak allows air to escape from the suspension system, leading to a loss of ride height, often noticeable after the vehicle has been parked.
- Common cause of sagging suspension.
- Can be slow (overnight) or rapid.
- Often audible as a hiss, or detectable with soap and water.
- Requires replacement of the affected air spring.
Memory trick: If it sags overnight, think 'slow leak' in the bag itself.