ASE A4 Suspension and SteeringSuspension System Diagnosis and RepairMedium
A vehicle with an electronically controlled air suspension system occasionally sags at one corner overnight, but typically returns to normal height after the engine is started and the compressor runs for a short period. There are no DTCs stored. Which of the following is the MOST likely cause?
- AFailed air suspension compressor
- BStuck open vent solenoid valve
- CMalfunctioning ride height sensor
- DIntermittent air spring leak
Show answer & explanationAnswer & explanation
Correct answer: D. Intermittent air spring leak
An intermittent air spring leak would allow air to slowly escape overnight, causing the vehicle to sag. Since the compressor can restore the height, it indicates the leak is slow enough for the compressor to overcome, and not a catastrophic failure of the compressor or a constantly open valve.
Why the other options are wrong
- A. A failed compressor would not be able to restore the vehicle's height, and would likely set a DTC.
- B. A stuck open vent solenoid valve would cause the air spring to deflate rapidly and continuously, and the compressor would struggle or fail to maintain height, likely setting a DTC.
- C. A malfunctioning ride height sensor would likely cause incorrect height adjustments or a persistent incorrect height, potentially setting a DTC, but not typically an overnight sag that resolves itself with compressor operation.
Intermittent Air Spring Leak
An intermittent air spring leak causes a slow loss of air pressure, leading to sagging, which can often be overcome by the air compressor.
- Often difficult to diagnose due to sporadic nature.
- Can be influenced by temperature changes or vehicle load.
- May not always set a DTC if the leak is slow.
Memory trick: Sagging overnight, but perks up with air, a sneaky leak is the culprit there.