AfterMarketNews AfterMarketNews Auto Care Pro AutoCareCareerHub Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service Speedville

Head Gasket Do’s and Don’ts

DO: Clean the holes. To ensure accurate torque values and to avoid cracking the cylinder block, clean any dust, dirt, oil and fluid from the cylinder block head bolt holes before installing the new head gasket and head bolts. Never lubricate the...

Read more...

Harmonic Dampeners: Why They Fail, What to Look For

Every time a cylinder fires, the crankshaft speeds up a very small amount for a short period of time. It is then slowed down as the next cylinder in the firing order compresses air and fuel for the next combustion event. The speeding up and slowing...

Read more...

Be Careful When Replacing That Diesel Air Filter

Modern passenger and light-duty diesels with ECMs have mass airflow sensors and precisely control fuel ­delivery. Key to the efficiency and lifespan of the diesel engine is the diesel air filter. A restricted air filter will not affect fuel economy but...

Read more...

TPMS Service Tip: Ask the Right Questions

If there is one piece of major advice for any tire tech facing a TPMS issue, it would be this: Test before you touch, and document the answers you get. Understanding the potential TPMS land mines can save time and money and eliminate frustrations. Get...

Read more...

False ABS Activation After Wheel Bearing Hub Replacement

Vehicles: All ABS-equipped vehicles Condition: Vehicle had wheel bearing hub replaced on one side. Repair Procedure: If you diagnose a bad hub bearing on one side of a vehicle and the ABS wheel speed sensor or tone ring is integral to the bearing,...

Read more...

Are you afraid of selling alignments?

I am starting to notice a trend when it comes to alignments. It’s not the vehicles that are changing, but rather the attitudes toward alignment services — and it happens at independent repair shops, franchise shops and even dealers. The alignment...

Read more...

Mazda: Performing Regular Undercar Maintenance

This month, we’ll take a look at brake and undercar service on the Mazda vehicle lineup, with the footnote that even though this type of work ­becomes routine when you have a preventive maintenance mindset, good work habits from beginning to end are...

Read more...

Import Automatic Transmission Diagnostics

Don’t be alarmed if you pull an automatic transmission trouble code when diagnosing a “check engine” warning light! Since the automatic transmission operation has a major effect on grams-per-mile exhaust emissions, you’re going to see the...

Read more...

Honda: Vehicle Won’t Move or Barely Moves

A customer brings in a vehicle that won’t move forward, ­­backward or both. Check first to see if it grinds or clicks. And does the speedometer read a lot higher than you’re actually going? Chances are the driveshaft is disengaged. This can...

Read more...

iATN Exceeds 2 Million Forum Messages

The number of messages in the professional automotive discussion forums of the International Automotive Technicians Network (iATN) exceeded 2 million in early December 2014, with the Shop Management and Technical Discussion forums being the most popular...

Read more...

Diagnosing Starter Misses

Contributing writer Gary Goms was called to a friend’s shop to help with a no-cranking condition on a 2006 Chevy Tahoe. After diagnosing a faulty PCM ground, locating the missing ground proved to be problematic. Find out how Gary solves The Case...

Read more...

Snap-on Adds Diagnostic Calculator To Website

Snap-on announces a new diagnostic calculator feature has been added to its website at http://diagnostics.snapon.com to help automotive repair technicians and shop owners determine how much profit they could be making by using a Snap-on diagnostic platform,...

Read more...
Home ASE Test Prep Air Ride: Compressor Diagnostics

Print Print Email Email

On most modern vehicles, the compressor and air ride control unit are very intelligent components. Most communicate with the Body Control Module (BCM) on a high-speed serial data bus. These systems have malfunction indicator lights on the dash and require the use of a scan tool to diagnose the system. 
 
Servicing modern air ride systems requires the right service information to interpret the “C” or chassis codes the air ride system can generate. A failure code and an illuminated dash light could be just a failure of the air ride module to communicate with the BCM. This could be due to electrical problems and not a leak in the air system or a compressor failure. 
 

With an enhanced or factory scan tool, it is possible to perform bi-direction tests on the compressor and valves during inspection. This can save you hours of diagnostic time waiting for a compressor to turn on and drain the battery or testing for an intermittent condition. Throwing parts at these vehicles without performing a proper diagnosis can result in an unhappy customer and lost productivity.  
 
The air ride module does more than control the ride height. The software controls the temperature of the compressor so it does not damage itself trying to inflate a leaking air bag. It can also change the characteristics of the air bag in response to how fast the vehicle is going and if it is in sport or towing mode. But most of all, it helps to filter out erroneous ride height readings so the best possible ride is achieved.  
  
Compressor Killers
Most passenger and light-truck compressors are diaphragm types that supply an oil-free air supply to the springs. A piston-type compressor can be found on applications that require a higher volume of air. 
 
Running the compressor for extended periods can over heat the compressor and damage the diaphragm or piston. It is very important to ensure that the source of air for the compressor is clean and as dry as possible.
 
In the air is moisture that can damage not only the compressor, but the valves. When air is compressed, the water vapor contained in the air is condensed into a liquid. If there is no means of removing the water from the system, it will find its way to all parts of the system causing corrosion damage or freezing.
 
Most systems have a dryer that is connected to the compressor outlet to absorb the water entering the system. The dryer contains a moisture-absorbing desiccant such as silica gel. The desiccant can hold a given amount of water and once the desiccant is saturated with water, it will allow water to pass into the system.
 
The dryers that are installed on most systems do not have an indicator that will show when it is saturated and no longer able to absorb water. An additional dryer with a moisture indicator can be added to the original equipment dryer. It can be installed in the supply line and placed in a position where a periodic check can be made.
 
Some systems have filters on the air intake for the pump. The filter removes airborne particles and acts as a noise muffler for the compressor. Some systems even send purged air back through the filter. This filter should be replaced with the compressor, and often this filter is attached to the compressor’s casing. 
 
Another killer of air-ride components is the compressor. As the compressor over heats and wears, it can send debris and oil to the rest of the system. This oil and debris can degrade the air bellows even after the compressor is replaced. This is why it is critical to flush the lines if a compressor has failed.  
 
Some systems have air reserve tanks or accumulators located in the most inconvenient locations, like below the C-pillar or next to the frame rail. If the system experiences a catastrophic failure of the compressor or air bladder, replacement or flushing of the reserve might be required.    
The health of the entire system depends on the quality of the air supply. It is rare for just one component of an air suspension to fail.  
Mechanical and Solenoid Valves
There are various combinations of both mechanical and solenoid valves.

The function of the mechanical or solenoid valve is to exhaust air from the spring(s). Each spring can have a valve. For the Lincoln air suspension system, there are five solenoid valves — one for each air spring or strut and one to exhaust air from the system. 
 
Most valves are used for a pair of load-assist springs. The compressor unit contains a one-way check valve to isolate it from the springs or a reservoir. The Lincoln compressor has a combination one-way check valve and exhaust solenoid valve to inflate or exhaust the springs individually. Whether the valve is mechanical or solenoid, it needs dry air to operate properly.
 
Plastic line is used to transport air in the system in sizes 1/4”, 3/8” and 1/2”. Most fittings are push-on O-ring type ranging in size from 1/8” to 3/8” Male NPT.
 
Air struts for some import vehicles can have even more complex valves, air chambers and accumulators on the strut body to keep the suspension taut under certain conditions. These types of struts will have both an air and electrical connection to control the valves on the strut and the hydraulic valves of the dampener.  
Dynamic Vehicle Trim
The Lincoln Continental Mark VIII is equipped with ride height sensors at each front wheel and one for the live rear axle at the driver’s side control arm. The sensors provide input to the controller for ride height. The suspension controller is programmed for two different ride heights.
 
Parked, the vehicle will maintain this height by compensating for passengers and luggage. When the vehicle is put into gear, the controller will raise the suspension ride height 0.75 inch (20 mm). When vehicle speed exceeds 63 mph (105 kph), ride height is lowered by 0.75 inch (20 mm). When vehicle speed decreases to 45 mph (72 kph), the vehicle ride height is increased. The differential between 45 and 63 mph provides a dead band where the system will not adjust ride height. This prevents the system from cycling with small changes in vehicle speed. With the ignition off and doors closed, the vehicle returns to parked height.
 
The rear air struts on GM vehicles are used to assist the conventional coil springs. Cadillac vehicles with Road Sensing Suspension (RSS) have an electrically operated hydraulic valve located at the base of the air shock. There are sensors located at each wheel that supply input to the ride controller that operates the valves in the air shock and front struts. The suspension height sensor is located on the driver-side control arm and the compressor is located in the rear suspension cradle.
Alternatives
There are suppliers that can provide economical replacements for both springs and struts. These alternatives replace the air ride components with springs and conventional ride control units. On some vehicles that still have 100,000 of miles of useable service left, these kits can offer an economical option for the driver. Also, some remanufacturers are willing to pay for the worn air ride shock or strut cores that come off the vehicle. In some cases, the core could be worth $300! 
The following two tabs change content below.

Andrew Markel

Andrew Markel is the editor of Brake & Front End and Servicio Automotriz magazines. He has been with Babcox Media for more than 12 years. He is a technician and former service writer and holds several automotive certifications from ASE and ­aftermarket manufacturers. He can be reached at [email protected]
Latest articles from our other sites:

Head Gasket Do’s and Don’ts

DO: Clean the holes. To ensure accurate torque values and to avoid cracking the cylinder block, clean any dust, dirt, oil and fluid from the cylinder block head bolt holes before installing the...More

Harmonic Dampeners: Why They Fail, What to Look For

Every time a cylinder fires, the crankshaft speeds up a very small amount for a short period of time. It is then slowed down as the next cylinder in the firing order compresses air and fuel for the next...More

TPMS Service Tip: Ask the Right Questions

If there is one piece of major advice for any tire tech facing a TPMS issue, it would be this: Test before you touch, and document the answers you get. Understanding the potential TPMS land mines can...More

False ABS Activation After Wheel Bearing Hub Replacement

Vehicles: All ABS-equipped vehicles Condition: Vehicle had wheel bearing hub replaced on one side. Repair Procedure: If you diagnose a bad hub bearing on one side of a vehicle and the ABS wheel speed...More

Mazda: Performing Regular Undercar Maintenance

This month, we’ll take a look at brake and undercar service on the Mazda vehicle lineup, with the footnote that even though this type of work ­becomes routine when you have a preventive maintenance...More

Import Automatic Transmission Diagnostics

Don’t be alarmed if you pull an automatic transmission trouble code when diagnosing a “check engine” warning light! Since the automatic transmission operation has a major effect on grams-per-mile...More

iATN Exceeds 2 Million Forum Messages

The number of messages in the professional automotive discussion forums of the International Automotive Technicians Network (iATN) exceeded 2 million in early December 2014, with the Shop Management and...More

Loosen Seized Fasteners with Lisle’s Small Fastener Remover

Use Lisle’s Small Fastener Remover (60530) with a pneumatic impact tool to loosen rusted or seized fasteners. A 3/4" open end wrench can be used to turn the socket while impacting the fastener. A...More