When the electronic suspensions with air springs were first featured 20 years ago on the Lincoln Continental and Mark VII, few people would have wondered that someday this new technology would produce a booming business for servicing air ride suspensions. But it has, and it’s a market that has no signs of deflation anytime soon. Here’s why:
Air springs and electronic ride controls offer a cushy, boulevard ride, but the ride doesn’t last forever. All air suspensions share a common The undervehicle environment is a harsh one that’s exposed to road splash, salt and debris. Rubber loses elasticity as it grows old, becomes hard and eventually cracks. After seven to 10 years of service, many of these older systems begin to develop leaks that let air to escape from the system. The same thing can occur to plastic air lines. Wiring connectors, solenoids, compressors and height sensors are also vulnerable to corrosion and vibration, which over time may result in failures that disrupt the normal operation of the air ride system.
Now comes the good side (or the bad part if you’re the car owner). When an air ride suspension system becomes flat, it can be very expensive to fix. OEM components are sky high and may not even be offered for some of the older applications. Remanufactured OEM and new aftermarket electronic air struts and compressors can provide a more cost-effective alternative for those who want to retain the full functionality of their air ride suspension. The other option is to change the original air springs and/or electronic struts or shocks with a conversion kit that includes conventional coil steel springs with ordinary struts or shocks.
AIR SUSPENSION CONVERSION KITS
Aftermarket conversion kits for the older vehicles with air ride suspensions have become a hot item in recent years since the kits provide a repair solution for cars that might otherwise be too expensive to fix. For example, a set of four new OEM air struts and a compressor for a 10-year-old 1994 Lincoln Continental retail for around $3,500. Add in the installation labor and it includes up to a lot of money to spend on a vehicle that is worth maybe $2,500. The same vehicle could be converted to a regular coil spring suspension for around $500 to $600 in parts, and it would probably be a lifetime repair (no future air leaks, compressor failures or electronic glitches to worry about).
On a Lexus, the numbers get even higher. The OEM air struts list for $1,100 per wheel! If the compressor also needs to be changed, the parts bill alone is around $5,800. By comparison, a conversion kit for this car typically sells for less than $800 and includes struts for all four wheels.
The only tradeoff of mounting a conversion kit is that a car will no longer have a cushy air ride suspension or be self-leveling. For many owners, that’s no big deal since many people say air ride suspensions are overly soft and allow too much wallow when cornering. They would actually prefer a firmer handling suspension. Others, though, might be reluctant to trade their air ride suspension for a conventional suspension. Even so, most of these people will probably realize it makes more sense to convert the suspension than to sink a pile of money into a vehicle that has already depreciated so much in value.
The ironic component about all of this is that some people will gladly spend thousands of dollars to transform their car into a pavement scraping “low rider” while others moan and complain about having to spend so much to fix their unintentional low rider due to fact that the air suspension has gone flat.
One other change that is usually needed when converting an air ride suspension is to disable or “fool” the system module. Procedures vary depending on the application, but may need removing a fuse, cutting a wire or splicing a resistor into a strut wiring harness to trick the module into thinking a solenoid or height sensor is still there when it is not. Ensure to review the conversion kit’s instructions or inspect other sources like manufacturer TSBs. Not following the proper procedures can effect other systems controlled by the body control module.
THE AIR SUSPENSION REPAIR OPTIONS
This creates another potential service opportunity: converting conventional suspensions to air ride suspensions. It’s not a traditional kind of repair job, but it is one that can be profitable, especially if you’re searching for a niche market to expand your business. A whole new generation of younger car owners are spending serious money these days customizing sport compact vehicles. The hot nameplates are Honda, Accord and Mitsubishi, but you will also see Chevy Cavaliers, Ford Focuses and other nameplates among their ranks.
The upgrades are done to improve ride and handling as much as cosmetics. The owners of sport compact vehicles will buy larger diameter 17- to 19-inch alloy wheels, sticky ultra low profile street performance tires, beefier sway bars, high pressure monotube gas struts and shocks, drilled and vented brake rotors, wings, spoilers, low restriction air intakes and mufflers, and lots of other bolt-on accessories.
Coil-over kits that change the stock struts are a popular upgrade for making suspension adjustments and lowering ride height, and now we’re seeing aftermarket coil-overs that use an air spring instead of a steel spring for a fully adjustable suspension on the fly. Some of these have an air strut suspension with adjustable height, rate and dampening. The kit includes air spring struts, compressor, dryer, lines and driver-adjustable control module.
Another air suspension repair option is to mount air shocks or air helper springs on your car if you use it for towing or hauling. The air shocks offer extra load carrying capacity to keep the rear end from sagging when your vehicle is heavily loaded. Mounting is easy and requires no wiring or other changes.
AGING CARS WITH AIR SUSPENSIONS
Cars that are prime candidates for air suspension repairs include older Lincoln Continental, Town Car, Mark VII and VIII, Ford Crown Vic, Mercury Grand Marquis, fullsize Chevy, Buick and Oldsmobiles, Cadillac Deville, Seville and Eldorado, various Chrysler models, Dodge Dynasty, older Jaguar models, Land Rover, Range Rover, Lexus, Lincoln Navigator, Ford Expedition and Ford F250 pickups, and Mazda MPV.
AIR RIDE BASICS
With an air suspension, hollow inflatable rubber bags (air springs) are used instead of ordinary coil steel springs or leaf springs. The rubber bags are flexible and contain a certain amount of give, so they help absorb and dampen bumps to better isolate the suspension from the vehicle’s occupants. Air springs also offer a variable spring rate and offer increased stiffness the more they are compressed.
On some cars, an air bladder is incorporated into a strut or shock to provide additional dampening and/or ride height control. Air shocks are one such example, and are often used on the rear for automatic load leveling. On some applications, a strut may have both a conventional steel spring with an additional air bladder on top to differ ride height and/or spring stiffness.
Most air suspensions and automatic load leveling systems use some type of height sensor to monitor ride height. When the suspension is lower than its normal ride height, the system module energizes a relay to turn on a compressor and pump air into the air springs, shocks or struts through solenoid valves. When the required ride height is reached, the module turns the compressor turns off and remains on standby until further corrections are required. If ride height is too high due to a heavily loaded vehicle has just been unloaded, the system module will open solenoids to vent air from the springs.
Keeping a consistent ride height is important because ride height affects wheel alignment, tire wear, handling, traction and the targeting of the headlights. It can even affect fuel economy at highway speeds. Some late-model SUVs with air ride suspensions automatically lower themselves an inch or two at highways speeds to improve their aerodynamics and lower wind resistance. The driver may equally have a ride height switch that lets him to increase ride height and ground clearance when driving off-road.
On many applications, the air ride system may remain active for a certain period of time after the engine has been turned off. The system continues to monitor ride height and may make corrections by adding or venting air as required. There may be a built-in delay so the corrections do not happen immediately when the occupants exit the car or unload the trunk.
Understanding the operating logic of an air ride suspension system is vital when trying to make a diagnosis because all of these systems are different. If you don’t understand the logic, you can’t always tell if the system is functioning correctly or not.
LINCOLN AIR SUSPENSION
On the older Lincoln systems, the control module monitors ride height for up to an hour after the ignition is turned off, venting pressure as required to maintain correct ride height. During this time it will lower, but not raise the vehicle. At the end of the hour, the compressor will kick in for up to 30 seconds to add air if ride height is low. After that, it shuts down and makes no further corrections until the ignition is turned back on.
When the ignition is turned on, the system will raise ride height if required, but not lower it. After 45 seconds, it will then make lowering corrections as required, but only if all the doors are closed. It will not make any corrections if the brake pedal is depressed. Once the system is in its “driving” mode, it averages input from the height sensors before making any adjustments in attitude. This stops the suspension from trying to compensate for every bump in the road. Only when a continuous high or low indication is present for more than 45 seconds will it react and make a change.
If a change in ride height isn’t realized within three minutes after the need is shown, the system warning lamp comes on and stays on as long as the ignition remains on. When the key is turned off, the warning lamp will go out and remain out unless the same problem is shown the next time the key is on.
AIR RIDE PROBLEMS
Air suspension problems are divided into one of three categories:
- Electrical – Issues with the height sensors, air spring solenoids, module control circuit, compressor relay, compressor or vent solenoid. These can be isolated by using the system’s self-diagnostic procedures (if available) and various volt/ohm checks. Service consists of replacing the faulty partrs or wiring, or readjusting the height sensors.
Electronic issues will usually set a fault code and turn on a warning light. On the older cars, there is usually a self-diagnostic procedure for reading the codes and doing self-tests. On newer cars, codes can usually be accessed with a scan tool. On the more sophisticated systems, you may require a professional bidirectional scan tool with the appropriate software to do system tests and to recalibrate height sensors.
On Cadillacs with the CVRSS electronic suspension, you can acquire codes by pressing the WARM and OFF buttons on the climate control system simultaneously. Refer to a manual for the code retrieval and clearing procedure when using the panel buttons.
- Air supply – Leaky or obstructed air lines, faulty compressor or spring solenoids. Diagnosis is made through the self-test and visual inspection. A bad compressor or solenoid must be changed, but damaged air lines can be repaired by splicing.
NOTE: One of the regular causes of compressor failure is air leaks (usually in the air springs or lines). If the compressor is constantly running, it’s going to work itself to an early death.
If you’re changing a compressor, the dryer should also be changed to protect the new unit from moisture. If the dryer is saturated with moisture, it can create backpressure that can overload and burn out a compressor.
- Air springs – Leaking, damaged, deflated or unfolded springs. Damaged springs must be changed as an individual assembly (replacement in pairs is not necessary with air springs). If unfolded, the spring must be carefully checked for cuts or cracks before it is reinflated.
AIR SUSPENSION REPAIR PRECAUTIONS
The first thing to bear in mind when servicing vehicles with electronic air suspensions is to watch out for those that are self-leveling – especially if the car is going to be raised on a lift to change the tires or work on the brakes.
If you have a Lincoln or a Ford Crown Victoria with an electronic air suspension, there’s a switch in the trunk to deactivate the system. If the system is not turned off, it will stay active after the ignition is switched off and try to level itself if you jack up and vehicle and raise the wheels off the ground. The sysem will vent air from the air springs in an attempt to level the suspension. When the car is then lowered back down, the suspension may go flat because there’s no air in the bags. Later systems are supposed to keep a minimum pressure in the springs so this doesn’t occur.
You also want to deactivate a self-leveling suspension when doing brake or suspension work. Why? Since you don’t want the suspension moving because a height sensor is telling the system module the cars is riding high.
Disconnecting a battery cable will equally deactivate an electronic self-leveling suspension, but you’ll also cut power to all the other onboard electronics. Disconnecting the battery will erase all the preset channels on your radio as well as the learned memory settings in the PCM and other modules. To stop this from occuring, use the air suspension deactivation switch (if one is provided) or find and pull the fuse that powers the self-leveling control module or air compressor. Don’t forget to reactive the system after repairs have been made otherwise the air suspension warning light will come on when the car is driven.
Another thing to keep in mind on Lincolns, Fords and other cars with full air spring suspensions is that the air springs support the weight of the chassis and are under pressure (25 psi minimum – unless the springs have gone flat). Do not vent an inflated spring or remove a spring solenoid unless the car is supported on a frame contact hoist, or the chassis is held by safety stands when the wheels are off the ground because the chassis will drop anytime air is allowed out of the springs.