Air suspension leaks: finding the leak, fitting and height calibration

Three kinds of sag

Locate the leak

• Compare the four corner heights on level ground with the same load.
• With the engine off, listen for a hiss near the wheel arches.
• Spray soapy water on the spring folds, top and bottom joints, line connectors, valve block and dryer vent.
• Inspect the spring for cracks, trapped stones and rubbing.
• Distinguish an oil leak (hydraulic fluid) from an air leak (bubbles).

Lifting and fitting

• Enable jack mode or switch off level control before lifting, where the model has it.
• On models without it, follow the manual; at least disconnect the compressor and valve block before lifting so the system cannot adjust.
• Support the body so the spring is not over-stretched or twisted.
• Mark the air lines before removal so they go back correctly.
• Check the top mount, bearing and dust boot.
• Tighten to the manual torque.

After fitting

• Height calibration: most models need a scan-tool routine; follow the manufacturer procedure.
• Wheel alignment where the work disturbed suspension geometry.
• Check compressor run count and dryer condition.
• Road test: raise and lower, different loads, rough surface.

When to replace the compressor or valve block

If the compressor still runs too often or cannot build pressure after the leak is fixed, test the compressor and relay.

A sticking or cross-leaking valve block leaves one corner out of control; confirm with scan-tool data.

Common mistakes

• Fitting a conventional shock absorber in place of an air strut.
• Replacing the spring without checking the valve block and lines.
• Delivering the car without height calibration.
• Damaging the spring during lifting.
• Ignoring the dryer, letting moisture into the system.