Air Suspension Issues Explained(+Top problems and Tips)

In this brief article we are going to discuss the general Air Suspension problems, what the causes are, and how these issues can be effectively dealt with.

What are the common air suspension issues in a car?

The most common Air suspension issues are:

  • Corner Sagging or Front/Rear Sagging
  • Suspension Leaning to one side
  • Suspension Dropping during overnight parking
  • Air suspension warning light

Air suspension systems provide a comfort level that is not possible with conventional steel spring suspensions. Air suspension systems, being complex, have traditionally been known to have issues on high mileage vehicles.

Air suspension system problems are significantly more expensive to fix as compared to conventional leaf or coil spring suspension systems. By the time these issues appear, the value of the vehicle would have dropped significantly so much that dealership fixes would probably cost as much as the vehicle’s resale price.

Vehicle owners therefore find it useful to understand their car air suspension system better and DIY the issues in order to avoid unnecessarily large repair bills.

Car Air Suspension Layout

The idea of a Vehicle Air suspension is surprisingly old. As early as 1901, the first air suspension was patented. A normal steel suspension would sag proportionate to the load it carries and therefore had a clear disadvantage when it came to carrying heavier loads. Beyond a certain point, the vehicle would ride on its axle since the heavy load would have completely bottomed-out the suspension springs. If the vehicle rides on the axle, effectively, the suspension travel has been reduced to nearly nothing.

So the first implementation of the air suspension idea was in a situation that involved the transportation of heavy and critical loads. The first air suspension designs were applied on trucks used during World War II with the intention of transporting heavy weapons and battle equipment and maintaining ride height at the same time, thus avoiding the suspension bottoming out.

Different manufacturers implemented their own unique version of an air suspension. Cadillac implemented air suspension on the Eldorado in 1953. Audi’s first air suspension was first introduced in 1999 in the A6 Avant as a variant called the A6 AllRoad Quattro. The Mercedes-Benz 300 SE was Daimler’s first attempt at using air bellows to replace the standard coil spring back in 1961.

Most OEM air suspensions basically would consist of 

  • An Air compressor that would either be powered directly by the engine or electrically to develop air pressure
  • A Solenoid valve Block Unit, that opens and closes air valves to each individual air spring
  • Reinforced Rubber Air Springs that inflated on being pressurized
  • An Air dryer or Desiccator that removed moisture from air in order to prevent corrosion and damage to compressor parts
  • An Electronic computer control unit (ECU) that controls the solenoid valve block and the compressor in order to maintain ride height automatically as well as manually, depending on the features provided by the OEM

Any issues with a car’s air suspension would invariably involve at least one of these five components.

Corner Suspension Sag or Front/Rear Sag

  • The Corner Sagging problem is the most common to all car Air suspension systems
  • The Symptom is that one of the Corner suspensions loses ride height after being parked overnight
  • In some cases, both sides (left and right) have lost height on either the front or the rear suspension

Root Cause:

  • There are 3 potential reasons for ride height loss on parking:
    • Faulty Ride height sensor
    • Air Spring Leakages
    • Valve-Block Defect
    • Faulty Air Compressor
    • Shock Absorber Leakage
  • Air leakage related suspension sagging generally is seen when the car is parked overnight and sometimes even over a period of days.
  • This fault can be confirmed using the manufacturer’s recommended Scanning/Diagnosis tool
  • Before starting the diagnostic scan, make sure to clear all Fault codes that have already been stored
  • Start the vehicle and try to lift the vehicle by selecting “Lift” option
  • The sequence to troubleshoot would involve looking at each of the suspension elements in the following order

Troubleshooting Corner Sagging: Leaking Shock Absorbers

  • Many OEMs incorporate suspension struts have the air spring as well as shock absorber integrated as one assembly. 
  • When the shock absorber fails, oil may not be visible on the outside
  • The leaked shock absorber oil gets into the air lines and creates blockages
  • The oil then stops the compressor from being able to pressurize and lift the air struts

Troubleshooting Corner Sagging: Compressor Failure

  • If the compressor ‘humming’ sound can be heard, and the suspension is not able to lift, it could be a case of a failed compressor
  • The Air Compressor tends to corrode over long-term use and internally wears out. Even if the compressor runs, it fails to develop the required pressure.
  • Although it would be best to replace the compressor, there are good chances that you could purchase a compressor ‘Rebuild Kit’ and attempt to Rebuild the compressor for your car.

Troubleshooting Corner Sagging: Ride Height Sensor Linkage

  • You need to Scan the Fault codes with the Ignition ON
  • Error codes that point to “Level Control system sensor” indicate that the ride height sensor linkage is a probable issue.
  • The faulty linkages need to be corrected or replaced.
  • After making the rectification, if there is a difference in height between the left and right side in the front and the back, it can be corrected by doing a height calibration. 
  • The steps to do a height calibration would be different for different cars. While some OEM’s have a mechanical lever adjustment, others come with an automatic computer-controlled calibration that can be done through the OEM Diagnostic Tool

Troubleshooting Corner Sagging: Air Spring Leakage

  • If the Ride height sensor linkages were not the issue, the next most probable cause would be an air leakage somewhere in the air suspension air circuit.
  • In the case of air leakages, the system does often detect and display the error code.
  • But, however, there have been many cases where confirmed leakages were not detected by Diagnostics.
  • Air springs are known to wear out and crack at the rubber bellow surface gradually after accumulating mileage. They generally would last 70K to 80K miles depending on usage.
  • In a high mileage vehicle, the air springs would be the first place to check for leakages.
  • Fill the Air springs by either 
    • Turning ON the ignition, or
    • In the Diagnostic tool, use the “Air Filling/Venting Set-up” Inspection/Test to fill air into the system, OR 
    • If the diagnostic method is not possible, then you can pressurize the air spring through the inlet using an external air compressor
  • Once the air springs are inflated, you need to spray springs with soap solution to check for leaking.
  • After spraying the soapy water solution, wait to see if there are white foam bubbles that stay at one spot even after wiping it with a finger.
  • In cases where the leak is major, you even hear a hissing noise coming from the leakage point and be able to locate it by ear.
  • Once you have confirmed that there indeed is a leak, the air spring has to be replaced. 

Troubleshooting Corner Sagging: Valve-Block Leakage or Defect

  • The valve block opens and closes valves to the individual air springs when it gets a signal from the air suspension ECU
  • When the valve block fails to appropriately open the valves to the air springs and supply air, the vehicle suspension sags
  • The DTC (Diagnostic Trouble Code) will mostly show up as a general fault in the air suspension. In some vehicles, the code is more specific and the DTC points to the valve block as the source of the fault
  • Locate the Valve block in the underbody of the vehicle
  • Use a soapy water spray to detect bubbles at the valve block air connector fittings
  • If there is a crack or damage at the valve block body, then it will need to be replaced.
  • Suppose there were no cracks/damages or leakages, then you need to check whether the valve is properly sending air to the individual air struts. This can be done using the diagnostic tool

Suspension Leaning to one side

  • The Air Suspension, sometimes, makes the car lean to one side due to daily use and wear in the suspension. But at the same time the suspension is not fully sagging.
  • The Self-adjust mechanism of the suspension does not Level the car Flat, or in other words, one side (either left or right) 
  • Ride height is self-adjusted by the Suspension System at a different ride height at one corner, compared to the opposite side.
  • In most cars, this sort of difference in ride height can be corrected by doing a height calibration. Depending on the vehicle, the calibration is done either manually by adjusting the ride height sensor levers or electronically, through the air suspension ECU using a diagnostic tool procedure.

Calibrating the Adaptive Air Suspension

  • Some OEM’s like Audi and BMW, nowadays, provide a calibration module in their Diagnostic Tool that you plug into the OBD 2
  • Using a calibration module, you can solve the Leaning Problem by inputting some simple measured values like wheel height from a body reference point into the tool interface.
  • The module then automatically calculates how much correction in needs to apply at each wheel so that the 4 corners are level

Suspension Dropping during overnight parking

  • Loss of ride height after long hours of parking is also a highly common symptom of suspension malfunction in most cars
  • Most of the cars’ Air suspension ECU would throw a warning indication on the dash continuously until the fault is rectified
  • When the suspension drops and is unable to raise itself, in many cases, the Air compressor would not be functioning

Troubleshooting Suspension Dropping: Electrical Fault

  • It would be best to Diagnose a suspension warning indication using a Scanner diagnostic Tool
  • If the Fault Code shows an electrical connector fault then first examine the Valve block connections
  • Remove and Check the Valve Block connector terminals for corrosion and clean if necessary
  • If the Fault Code points to the vehicle leveling front sensor, it mostly also shows which of the sensors is at fault
  • Start by first checking for voltage reading at the faulty sensor through the diagnostic tool, and then checking the electrical continuity at the faulty height sensor connector
  • If needed, replace the particular faulty corner height sensor

Air Suspension warning light

  • Most cars flash a yellow suspension warning light to show a fault in the ride height adjustment
  • In many cases, when pressing the ride height adjust button, the height does not change
  • In many other cases, one or more of the Corner suspensions loses ride height after parking

Root Cause:

  • The loss of suspension height, could be due to multiple reasons, the two main ones being:
  • Air leakages somewhere in the system
  • Valve Blockages
  • A slow air leakage causes sagging generally when the car is parked overnight and sometimes even over a period of days.
  • This fault can be confirmed using the OE Scanning/Diagnosis tool
  • Before starting the scan clear all Fault codes that have already been stored
  • Start the vehicle and change suspension height to lift the vehicle by selecting “Lift” option

Troubleshooting Suspension Warning Light: Leakage

  • You need to Scan the Fault codes while the vehicle suspension is trying to lift itself. This can be started by setting the suspension to ‘Lift’ mode.
  • In the case of leakages, the system does detect and display the concerned error code
  • Air springs are known to wear out and crack at the rubber bellow surface gradually after accumulating mileage. They generally would last 70K to 80K miles depending on usage.
  • In a high mileage vehicle, the air springs would be the first place to check for leakages.
  • Fill the Air springs by either 
    • Turning ON the ignition, or
    • In the Diagnostic tool, use the “Air Filling/Venting Set-up” Inspection/Test to fill air into the system, OR 
    • If the diagnostic method is not possible, then you can pressurize the air spring through the inlet using an external air compressor
  • After spraying the soapy water solution, wait to see if there are white foam bubbles that stay at one spot even after wiping it with a finger.
  • In cases where the leak is major, you even hear a hissing noise coming from the leakage point and be able to locate it by ear.
  • Once you have confirmed that there indeed is a leak, the air spring has to be replaced.

Troubleshooting Suspension Warning Light: Valve-Block Leakage

  • The DTC (Diagnostic Trouble Code) will mostly show up pointing to a malfunction in the Valve Block
  • Use a soapy water spray to detect bubbles at the valve block air connector fittings
  • If there is a crack or damage at the valve block body, then it will need to be replaced.

Tips on Replacing the Air Springs

  • Before removing the air spring for replacement, be sure to relieve the air pressure from it at the valve block, which is located in the underbody near the rear bumper.
  • Relieve the left or right air spring valve by loosening the connector gradually. If this is done suddenly, then you could risk damaging the O-rings within the air connector fitting.
  • While replacing the Air Spring, be sure to cut off the portion of the line that was squeezed or stretched in the old fitting after disconnecting. The reason being that the old used portion  of the air line could crack and cause a potential leak.

Pro-Tip:

  • ?In most cars, aftermarket brand replacement bellows tend to give a higher service life as compare to the original OE spare part
  • Moreover, some aftermarket replacement parts also come with a lifetime warranty instead of a limited warranty offered by manufacturer

Tips on Rebuilding the Air Suspension Compressor

  • An air compressor is expensive to replace new, and in many cases almost close to the resale value of the car
  • Many owners try to DIY the compressor with repair kits available from small companies
  • To check for compressor issues, you need to dismantle it and examine the Piston, Cylinder and Piston ring condition.
  • The compressor seizes mostly due to overheating. The parts that get damaged first are the Piston Ring and the O-seals that make the compressor air-tight. A repair kit would mostly consist of a set of Piston rings and a set of o-rings that suit the particular OE compressor unit.

The rebuild option does come with risks as there could be issues in the compressor other than just the piston and rings.

Conclusion

In this brief article we have discussed the general Air Suspension problems, what the causes are, and how these issues could be effectively dealt with.

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