Air suspension compressor and air spring for front were replaced but still not working correctly

Would need to find out what's wrong first ! The air shock could be bad , ride hight sensor , air line could be broke etc...
The air suspension compressor assembly has the ability to detect faults and indicate the appropriate fault code via a blink code on the inflator switch LED. Is the light on ?
The air suspension compressor assembly will indicate the code when the condition that caused the code is current. In some instances the air suspension compressor assembly may set a flag that requires the ASCM to be reset. The ASCM will reset on its own after the ignition has been turned off for more than 2 1/2 hours or if the air suspension fuse has been removed with the ignition key turned off.

Perform a visual inspection checking for the following:
• Disconnected or damaged air lines.
• Disconnected or damaged air sensor link.
• Disconnected or damaged electrical harness

Trim Height Uneven or Low
Step
Action
Yes
No
Schematic Reference: Suspension Controls Schematics
1
Did you perform the Air Suspension Diagnostic System Check?
Go to Step 2
Go to Diagnostic System Check - Air Suspension
2
Did you review the Air Suspension Description and Operation?
YES - Go to Step 3
NO - Go to Air Suspension Description and Operation
3
Perform a visual inspection checking for the following:
• Disconnected or damaged air lines.
• Disconnected or damaged air sensor link.
• Disconnected or damaged electrical harness.
Did you find and correct the condition?
YES - Go to Step 9
NO - Go to Step 4
4
Cycle the rear compartment inflator switch.
Does the compressor operate?
YES - Go to Step 5
NO - Go to Inflator Inoperative
5
Check the vehicle D-height . Refer to Trim Height Specifications and Trim Height Inspection .
Are the measurements within the specified values?
YES - Go to Step 6
NO - Go to Step 7
6
Perform the air suspension air leak diagnosis. Refer to Air Suspension Air Leak Diagnosis .
Did you find and correct the condition?
YES - Go to Step 10
NO - System OK
7
Recalibrate the air suspension level sensors. Refer to Rear Air Spring Level Sensor Calibration .
Did you find and correct the condition?
YES - Go to Step 10
Go to Step 8
8
Replace the air spring sensor. Refer to Air Spring Leveling Sensor Replacement .
Did you find and correct the condition?
YES - Go to Step 10
NO - Go to Step 9
9
Subtract the Service Preferred Trim Height specification from the value obtained in step 12 of the Air Spring Leveling Sensor replacement procedure.
Add the value to the Service Preferred Trim Height specification. This is the adjusted D-Height measurement.
Repeat the Air Spring Calibration procedure using this value in place of the D-Height specification in step 7 of the Air Spring Calibration procedure.
YES - Did you find and correct the condition?
NO - Go to Step 10
--
10
Operate the system in order to verify the repair.
Did you correct the condition?
System OK
--

Does your car have air suspension or coil springs. If you change the air springs and it still is low, it may be the air compressor or limit switches. But the front springs are coil and not air, so I see no reason it should ride low if you replaced with the correct parts. Now if you replaced the front shocks and not the coil springs, then the coil springs may need to be replaced.

There has been a service bulletin for that type of concern. Here is what it states.









Suspension - Rear Suspension Is Low/Sagging/Uneven

Notes




ENGINEERING INFORMATION

Bulletin No.: 06-03-09-006B

Date: December 15, 2008
Subject:
EI06006 - Rear Suspension Uneven, Sagging, Low (Recalibrate Air Spring Sensor)

Models:
2006-2007 Buick Rainier
2006-2007 Chevrolet TrailBlazer SS
2006-2007 GMC Envoy, Envoy XL
2006-2007 Saab 9-7X


with Suspension Pkg - Rear Load Leveling (RPO G67)

Supercede:

This bulletin is being revised to update the labor operation in the warranty information. Please discard Corporate Bulletin Number 06-03-09-006A (Section 03 - Suspension).

Condition

Some customers may comment on the rear suspension being uneven or sagging.

Correction

DO NOT REPLACE THE COMPRESSOR.

Based on technician feedback, engineering has determined that the customer's concern can be corrected by recalibrating the air spring sensor. Refer to the Trim Height Uneven or Low diagnostics and Air Spring Sensor Calibration procedure found in SI.

make sure you don't have an air leak at the springs or the compressor. but you may want to have the air suspension module checked for fault codes. the module itself may be the issue not processing the inputs correctly and mis-leveling the vehicle.

If I'm understanding the question correctly, the problem is the rear is stuck in the "jacked up" position. If you start the car and after a short while the check suspension message comes on, most likely the problem is a rusted corroded vent solenoid in the compressor. When this solenoid sticks closed, the air can't vent to the atmosphere. Keep in mind this problem is a very common one and the root cause is excessive moisture in the system. While replacing the compressor/dryer would get it working normally again, if the moisture problem isn't addressed, the replacement compressor WILL BE short lived as well. RECAP: Short term....replace the compressor/dryer. Long Term....replace the compressor/dryer, then in 30 days replace the dryer only....then again in 6 months. Want to be done it those problems forever? Do a Lincoln Town Car Air Suspension Conversion on your car and be done with those expensive repairs forever!......for less than the cost of a replacement compressor.

why do you want to replace it? As air is exhausted through it, it dires it out for the next use. it's part of compressor assembly.

1996 cont'l The air suspension system includes the following major components:

• Air compressor to supply air to the air springs (part of front spring and shock and rear spring and shock absorber assemblies
• Front spring and shock (3C098) and rear spring and shock absorber (5A965) at each corner of the vehicle
• Four linear air suspension height sensors (5359): two rear and two front height sensors to maintain the vehicle at the proper ride height; only LH rear height sensor is used for air suspension.
• Dual-mode front spring and shock and rear shock absorber assemblies with internal actuator.

All system functions are controlled by vehicle dynamics control module (5A919). This control module receives inputs from several different sources. These inputs include:

• vehicle speed via multiplex communication network
• ignition switch position
• door position via multiplex communication network
• height sensor position
• air suspension service switch
• engine rpm via multiplex communication network
• ride and steering personality settings via multiplex communications network

Communications monitor system operation and allow diagnosis of any concerns that may develop in the system. System monitoring for the driver's use is provided through the instrument panel mounted message center indicator (10D898).

• Diagnosis communication for the service technician is provided through the data link connector (14489) (DLC) under the instrument panel and Rotunda New Generation Star (NGS) Tester 007-00500 or equivalent.

The message center indicator will display AIR LEVELING DISABLED or CHECK RIDE CONTROL if the suspension system is not turned on or the vehicle dynamics control module detects a concern. If air leveling system disabled is displayed, check that air suspension service switch is in the ON position.
----------------------------------------------------------
Solenoid Valve Vent The vent solenoid valve operates as follows:

• The vent solenoid valve allows air to escape from the system during venting corrections.
• The valve is located in the air compressor cylinder head and shares a common electrical connector with the motor.
• The valve is enclosed in the cylinder head casting, which forms an integral valve housing that allows the valve tip to enter the pressurized side of the system.
• Air leakage past the valve tip is prevented by an O-ring seal.
• The vent solenoid valve opens when a corner of the vehicle is high and the vehicle dynamics control module (5A919) determines lowering is required.
• When the vent solenoid valve is opened, it provides an escape route for pressurized air.
• However, the vehicle will not lower unless the air spring solenoid valves (5311) are also opened to allow air to leave the springs.
• Lowering the vehicle corners requires the vehicle dynamics control module to open two solenoid valves, the vent and one air spring solenoid.
• Air is exhausted from the spring and vents through the compressor air drier (5346).

---------------------------------------------------------------------------------------------
Section 04-05: Suspension, Computer Controlled 1996 Continental Workshop Manual
REMOVAL AND INSTALLATION Air Compressor and Drier Assembly Removal

1. Turn air suspension service switch OFF.
   

1. Disconnect electrical connector located on the air compressor.
   

1. Disconnect two air lines from compressor air drier.
   

1. Remove three fasteners retaining air compressor and drier assembly to radiator support, frame rail and fender apron.
   

year?

SECTION 204-05: Vehicle Dynamic Suspension — 4-Wheel 2003 Expedition/Navigator Workshop Manual
DESCRIPTION AND OPERATION Vehicle Dynamic Suspension The four wheel air suspension system is comprised of the following components:

• service switch
• control module
• two front height sensors
• one rear height sensor
• compressor and drier assembly (includes vent solenoid)
• air lines
• front and rear air spring and shock absorber assemblies
• four air spring solenoids

-------------------------------------------------------------------------------
Principles of Operation
The 4-wheel air suspension (4WAS) module commands changes in vehicle height that are necessary for both the load leveling and the vertical height adjustment features.
The 4WAS load leveling feature automatically makes adjustments in vehicle height so that the vehicle is always at trim height, and that constant front-to-rear vehicle attitudes are maintained over the load range of the vehicle. Adjustments in height that are necessary to correct height differences between the vehicle left and right sides for the 4WAS system are restricted to what can be reliably achieved with three height sensors.
The height adjustment feature has three vehicle heights within a two-inch span:
Kneel height — improves the ease of entering and exiting by lowering the vehicle one inch below the trim height in the front and rear when the vehicle ignition is in the OFF or LOCK positions and the vehicle is stationary.
Trim height — normal vehicle ride position; vehicle moves to trim position when the ignition is ON, when the transmission is initially shifted to DRIVE or REVERSE mode, when all doors are closed or when speed of more than 24 km/h (15 mph) is detected.
Off-road height — improves ground clearance by raising the vehicle one inch above trim height in the front and rear when the vehicle is at 4x4 low modes and the vehicle speed is less than 40 km/h (25 mph).
The 4WAS module uses the universal bus protocol, (UBP), module communications network for sending and receiving various signals with the exception of speed, information from the three height sensors, and the air suspension service switch. For additional information about UBP, refer to Section 418-00 .
The 4WAS system holds vehicle height when any door or rear hatch is opened. The system stores front and rear vehicle height the moment any door is detected open. The system then maintains this height regardless of the addition or removal of a load. The system returns to its commanded height when all doors are closed or vehicle speed exceeds 24 km/h (15 mph).

---------------------------------------------------------------
Air Suspension Service Switch
The air suspension service switch signal is needed to wake up the 4WAS module. Without the module receiving this signal, the 4WAS system is inoperative at speeds below 24 km/h (15 mph) and will not react when the vehicle is raised or lowered. At speeds above 24 km/h (15 mph), the system will be active as if the air suspension service switch is in the ON position.
---------------------------------------------------------
Air Compressor
The air compressor:

• consists of the compressor and vent solenoid; neither are replaceable as individual items.
• is a single cylinder electric motor driven unit that provides pressurized air as required.
• is powered by a solid state relay, which is controlled by the 4WAS module.
• passes pressurized air through the compressor air drier that contains silica gel (a drying agent). Moisture is then removed from the compressor air drier when vented air passes out of the system during vent operation.
• has a single port drier that can be replaced separately.

The vent solenoid:

• allows air to escape from the system during venting actions.
• is part of the air compressor cylinder head.
• shares a common electrical connector with the air compressor motor.
• is enclosed in the cylinder head casting, which forms an integral valve housing that allows the valve tip to enter the pressurized side of the system.
• has an O-ring seal that prevents air leakage past the valve tip.
• opens when the 4WAS module determines that lowering is required.
• provides an escape route for pressurized air when system pressures exceed safe operating levels.
• has a 1034 kPa (150 psi) internal relief valve.
• is installed with the air compressor as a unit.

Air Spring
The 4WAS system has front and rear air springs. The air springs provide a varying spring rate proportional to the system's air pressure and volume. The air suspension system regulates the air pressure in each air spring by compressing and venting the system's air. Increasing air pressure (compressing) raises the vehicle; decreasing air pressure (venting) lowers the vehicle. Vehicle height is maintained by the addition and removal of air in each air spring through an air spring solenoid installed in the upper spring cap and energized through the 4WAS module command.
Air Lines and Fittings
NOTE: Apply a soapy water solution to the air lines to verify the location of air leaks. If the air lines are cut, ruptured or leaking, a service repair kit is available.
Nylon air lines with quick connect fittings connect to the air compressor and air spring solenoids. The compressor assembly output line is divided by the use of a fitting to supply the front and rear air springs. Fittings are also used to divide the air supply to the RH and LH air spring solenoids.
Air Suspension Height Sensors
There are two sensors used for the front suspension and one sensor used for the rear suspension. The sensors send a voltage signal to the 4WAS module. The output ranges from approximately 4.50 volts at minimum height (when the vehicle is low or in full jounce) to 0.50 volt at maximum height (when the vehicle is high or in full rebound). The sensors have a usable range of ± 45° compared to total suspension travel of 196 mm (7.84 in) at the front wheels and 240 mm (9.6 in) at the rear wheels. Therefore, the sensors are mounted to the suspension at a point where full suspension travel at the wheel is relative to the travel at the height sensor. The front height sensors are mounted to the frame and the links are attached to the upper arm ball studs. The rear height sensor is mounted to the frame and the link is attached to the rear lower arm ball stud.
When the height sensor indicates that the vehicle is lower than trim under normal driving conditions, the air compressor will turn on and pump compressed air to the system. When the sensor indicates that the vehicle is raised above trim under normal driving conditions, this will cause the air to be vented from the system to lower the vehicle to its trim height level.
Compressor Relay
A solid state relay is used in the air suspension system for compressor control. The relay incorporates a custom power metal oxide semi-conductor field effect transistor (MOSFET) and ceramic hybrid circuitry. The relay switches high current loads in response to low power signals and is controlled by the logic of the 4WAS module.
The compressor solid state relay is energized by the 4WAS module to have high current flow from the battery to the compressor motor.
4-Wheel Air Suspension (4WAS) Module
NOTE: The 4WAS module must receive a ride height adjustment calibration and must pass a pneumatic test when it is installed new or swapped.
The 4-wheel air suspension (4WAS) module controls the air compressor motor (through a solid state relay), all air spring solenoids, and provides power to front and rear height sensors. The 4WAS module also controls vehicle height adjustments by monitoring the three height sensors and other universal bus protocol (UBP) signals. The 4WAS module conducts all fail-safe and diagnostic strategies, and contains self-test and communication software for testing the vehicle and related components.
The 4WAS module monitors and controls the air suspension system through a 26-pin, two-way connector. The 4WAS module is keyed so that it cannot be plugged into an incorrect harness. There are two harness hardshell connectors and each is uniquely colored and keyed to prevent reversed connections.
-----------------------

• The air compressor continuously cycles with the ignition switch in the OFF position and no DTC is set

• Circuitry.
• Air suspension relay.
• 4WAS module.

start here

The air suspension system is designed to improve ride, handling and general vehicle performance for static, on-road and off-road driving condition:

• Ride is improved by using an air type spring (the soft ride is inherent).
• Handling is improved by maintaining constant vehicle attitude.

The system consists of unique rear air springs, air compressor, air lines, air spring solenoids, height sensor, air suspension control module, attachments and associated signals derived from both driver and road inputs. With these components and signals, the air suspension control module commands changes in vehicle height that are necessary for the load leveling features.
The load leveling feature rear air suspension (RAS) systems shall automatically make adjustments in vehicle height so that the vehicle is always at trim height and constant front-to-rear vehicle attitudes are maintained over the expected load range of the vehicle. Adjustments in height that are necessary to correct height differences between the vehicle's left and right sides for RAS system shall be restricted to what can be reliably achieved with one air suspension height sensor.
The system uses one air suspension height sensor, a steering sensor, generic electronic module (GEM) transfer case inputs, and other vehicle sensors to measure driver and road inputs. The system changes vehicle height using an air compressor, two air lines, and the use of an air spring with an air spring solenoid.
The air suspension system holds vehicle height when the rear hatch or any door is opened. The system stores rear vehicle height the moment any open door is detected. The system then maintains this height regardless of the addition or removal of a load. The system will return to its commanded height when all doors are closed and the vehicle speed exceeds 16 km/h (10 mph).
Air Suspension Switch
The air suspension switch is located behind the RH kick panel on a mounting bracket. The switch interrupts power to the air suspension control module.
The air suspension switch supplies a signal to the air suspension control module. Without the air suspension control module receiving this signal the load leveling system is inoperative and will not react when rear of the vehicle is raised or lowered. If the air suspension system is disabled by turning off air suspension switch, a "CHECK SUSP" will appear in the RH corner of the instrument cluster with the ignition in the run position.
Air Compressor
The RAS air compressor:

• Is not interchangeable with four wheel air suspension (4WAS) compressor.
• Consists of the compressor and vent solenoid; neither are replaceable as individual items.
• Is mounted in the engine compartment between the washer fluid bottle and headlamp (RH front corner).
• Is a single cylinder electric motor driven unit that provides pressurized air as required.
• Is powered by a solid state relay, controlled by the air suspension control module.
• Passes pressurized air through the compressor air drier that contains silica gel (a drying agent). Moisture is then removed from the compressor air drier when vented air passes out of the system during vent operation.
• Air drier has a single port and is not interchangeable with 4WAS compressor air drier.
• Air drier may be replaced separately.
• Incorporates a snorkle that may be replaced separately.

The vent solenoid:

• Allows air to escape from the system during venting actions.
• Is located in the air compressor cylinder head.
• Has a 160 psi internal relief valve.
• Shares a common electrical connector with the air compressor motor.
• Is enclosed in the cylinder head casting, which forms an integral valve housing that allows the valve tip to enter the pressurized side of the system.
• Has an O-ring seal that prevents air leakage past the valve tip.
• Opens when the air suspension control module determines lowering is required.
• Provides an escape route for pressurized air that opens when system pressures exceed safe operating levels.
• Is replaced with the air compressor as a unit.

Air Spring
RAS vehicles use air springs in the rear. The air springs provide a varying spring rate proportional to the systems air pressure and volume. The air suspension system regulates the air pressure in each air spring by compressing and venting the system air. Increasing air pressure (compressing) raises the rear of the vehicle while decreasing air pressure (venting) lowers the rear of the vehicle. Vehicle height is maintained by the addition and removal of air in each air spring through an air spring solenoid installed in the upper spring cap and energized through the air suspension control module.
The air springs are mounted between the axle spring seats and the frame upper spring seats.
The two air springs replace the conventional rear coil springs.
Air Suspension Height Sensor
When the air suspension height sensor indicates that the rear of the vehicle is lower than trim under normal driving conditions, the air compressor will turn on and pump compressed air to the air springs. When the sensor indicates that the rear of the vehicle is raised above trim under normal driving conditions, this will cause the air to be vented from the air springs to lower the vehicle back to its trim height level.
One air suspension height sensor is mounted on the vehicle. The air suspension height sensor sends a voltage signal to the air suspension control module. The output ranges from approximately 4.75 volts at minimum height (when the vehicle is low or in full jounce), to 0.25 volts at maximum height (when the vehicle is high or in full rebound). The air suspension height sensor has a useable range of 80 mm (3 in) compared to total suspension travel of 200-250 mm (8 to 10 in) at the wheel. Therefore, the air suspension height sensor is mounted to the suspension at a point where full rear suspension travel at the wheel is relative to 80 mm of travel at the air suspension height sensor. The air suspension height sensor is attached between the No. 5 frame crossmember (upper socket) and the panhard rod (lower socket). Replace the air suspension height sensor as a unit.
Compressor Relay
The compressor relay is energized by the air suspension control module to allow high current to flow from the battery to the compressor motor.

• A solid state relay is used in the air suspension system for air compressor control. The relay incorporates a custom power metal oxide semi-conductor field effect transistor (MOSFET) and ceramic hybrid circuitry. The relay switches high current loads in response to low power signals and is controlled by the logic of the air suspension control module.

Air Suspension Control Module
NOTE: The 4WAS air suspension control module is used for the RAS system. The internal processor recognizes external circuitry to determine if it is installed in a 4WAS or a RAS equipped vehicle.
NOTE: The air suspension control module is calibrated with information from the air suspension height sensor. A new or exchanged air suspension control module requires a ride height adjustment calibration process to be performed.
The air suspension control module controls the air compressor motor (through a solid state relay), and the air spring solenoids. The air suspension control module also provides power to the air suspension height sensor. The air suspension control module controls vehicle height adjustments by monitoring the air suspension height sensor, vehicle speed, a steering sensor, acceleration input, the door ajar signal, transfer case signals, and the brake pedal position (BPP) switch. The air suspension control module also conducts all fail-safe and diagnostic strategies and contains self-test and communication software for testing of the vehicle and related components.
The air suspension control module is mounted in the passenger compartment inside the instrument panel above the radio and temperature controls.
The air suspension control module monitors and controls the air suspension system through a 32-pin two-way connector. The air suspension control module is keyed so that the air suspension control module cannot be plugged into an incorrect harness. There are two sides of the harness connection to the air suspension control module. Each is uniquely colored and keyed to prevent reversing the connections.
Air Suspension Diagnostic Connector
The air suspension diagnostic connector is used to aid the technician in diagnosing the air suspension system. It is also used to vent the system of compressed air when air suspension system components need to be repaired or replaced. The air suspension diagnostic connector is located under steering column.

this will get you started. report back on progress and we'll go from there. There is a diagnostic test that will provide codes I think. I will look.

The system consists of unique rear air springs, air compressor, air lines, air spring solenoids, height sensor, air suspension control module, attachments and associated signals derived from both driver and road inputs. With these components and signals, the air suspension control module commands changes in vehicle height that are necessary for the load leveling features.
The load leveling feature rear air suspension (RAS) systems shall automatically make adjustments in vehicle height so that the vehicle is always at trim height and constant front-to-rear vehicle attitudes are maintained over the expected load range of the vehicle. Adjustments in height that are necessary to correct height differences between the vehicle's left and right sides for RAS system shall be restricted to what can be reliably achieved with one air suspension height sensor.
The system uses one air suspension height sensor, a steering sensor, generic electronic module (GEM) transfer case inputs, and other vehicle sensors to measure driver and road inputs. The system changes vehicle height using an air compressor, two air lines, and the use of an air spring with an air spring solenoid.
The air suspension system holds vehicle height when the rear hatch or any door is opened. The system stores rear vehicle height the moment any open door is detected. The system then maintains this height regardless of the addition or removal of a load. The system will return to its commanded height when all doors are closed and the vehicle speed exceeds 16 km/h (10 mph).
Air Suspension Switch
The air suspension switch is located behind the RH kick panel on a mounting bracket. The switch interrupts power to the air suspension control module.
The air suspension switch supplies a signal to the air suspension control module. Without the air suspension control module receiving this signal the load leveling system is inoperative and will not react when rear of the vehicle is raised or lowered. If the air suspension system is disabled by turning off air suspension switch, a "CHECK SUSP" will appear in the RH corner of the instrument cluster with the ignition in the run position.
Air Compressor
The RAS air compressor:

• Is not interchangeable with four wheel air suspension (4WAS) compressor.
• Consists of the compressor and vent solenoid; neither are replaceable as individual items.
• Is mounted in the engine compartment between the washer fluid bottle and headlamp (RH front corner).
• Is a single cylinder electric motor driven unit that provides pressurized air as required.
• Is powered by a solid state relay, controlled by the air suspension control module.
• Passes pressurized air through the compressor air drier that contains silica gel (a drying agent). Moisture is then removed from the compressor air drier when vented air passes out of the system during vent operation.
• Air drier has a single port and is not interchangeable with 4WAS compressor air drier.
• Air drier may be replaced separately.
• Incorporates a snorkle that may be replaced separately.

The vent solenoid:

• Allows air to escape from the system during venting actions.
• Is located in the air compressor cylinder head.
• Has a 160 psi internal relief valve.
• Shares a common electrical connector with the air compressor motor.
• Is enclosed in the cylinder head casting, which forms an integral valve housing that allows the valve tip to enter the pressurized side of the system.
• Has an O-ring seal that prevents air leakage past the valve tip.
• Opens when the air suspension control module determines lowering is required.
• Provides an escape route for pressurized air that opens when system pressures exceed safe operating levels.
• Is replaced with the air compressor as a unit.

Air Spring
RAS vehicles use air springs in the rear. The air springs provide a varying spring rate proportional to the systems air pressure and volume. The air suspension system regulates the air pressure in each air spring by compressing and venting the system air. Increasing air pressure (compressing) raises the rear of the vehicle while decreasing air pressure (venting) lowers the rear of the vehicle. Vehicle height is maintained by the addition and removal of air in each air spring through an air spring solenoid installed in the upper spring cap and energized through the air suspension control module.
The air springs are mounted between the axle spring seats and the frame upper spring seats.
The two air springs replace the conventional rear coil springs.
Air Suspension Height Sensor
When the air suspension height sensor indicates that the rear of the vehicle is lower than trim under normal driving conditions, the air compressor will turn on and pump compressed air to the air springs. When the sensor indicates that the rear of the vehicle is raised above trim under normal driving conditions, this will cause the air to be vented from the air springs to lower the vehicle back to its trim height level.
One air suspension height sensor is mounted on the vehicle. The air suspension height sensor sends a voltage signal to the air suspension control module. The output ranges from approximately 4.75 volts at minimum height (when the vehicle is low or in full jounce), to 0.25 volts at maximum height (when the vehicle is high or in full rebound). The air suspension height sensor has a useable range of 80 mm (3 in) compared to total suspension travel of 200-250 mm (8 to 10 in) at the wheel. Therefore, the air suspension height sensor is mounted to the suspension at a point where full rear suspension travel at the wheel is relative to 80 mm of travel at the air suspension height sensor. The air suspension height sensor is attached between the No. 5 frame crossmember (upper socket) and the panhard rod (lower socket). Replace the air suspension height sensor as a unit.
Compressor Relay
The compressor relay is energized by the air suspension control module to allow high current to flow from the battery to the compressor motor.

• A solid state relay is used in the air suspension system for air compressor control. The relay incorporates a custom power metal oxide semi-conductor field effect transistor (MOSFET) and ceramic hybrid circuitry. The relay switches high current loads in response to low power signals and is controlled by the logic of the air suspension control module.

Air Suspension Control Module
NOTE: The 4WAS air suspension control module is used for the RAS system. The internal processor recognizes external circuitry to determine if it is installed in a 4WAS or a RAS equipped vehicle.
NOTE: The air suspension control module is calibrated with information from the air suspension height sensor. A new or exchanged air suspension control module requires a ride height adjustment calibration process to be performed.
The air suspension control module controls the air compressor motor (through a solid state relay), and the air spring solenoids. The air suspension control module also provides power to the air suspension height sensor. The air suspension control module controls vehicle height adjustments by monitoring the air suspension height sensor, vehicle speed, a steering sensor, acceleration input, the door ajar signal, transfer case signals, and the brake pedal position (BPP) switch. The air suspension control module also conducts all fail-safe and diagnostic strategies and contains self-test and communication software for testing of the vehicle and related components.
The air suspension control module is mounted in the passenger compartment inside the instrument panel above the radio and temperature controls.
The air suspension control module monitors and controls the air suspension system through a 32-pin two-way connector. The air suspension control module is keyed so that the air suspension control module cannot be plugged into an incorrect harness. There are two sides of the harness connection to the air suspension control module. Each is uniquely colored and keyed to prevent reversing the connections.
Solenoid Valve, Air Spring
WARNING: Never rotate an air spring solenoid valve to the release slot in the end cap fitting until all pressurized air has escaped from the spring to prevent damage or injury.
The air spring solenoid:

• allows air to enter and exit the air spring during leveling operations.
• is electrically operated and controlled by the air suspension control module.

Air Suspension Diagnostic Connector
The air suspension diagnostic connector is used to aid the technician in diagnosing the air suspension system. It is also used to vent the system of compressed air when air suspension system components need to be repaired or replaced. The air suspension diagnostic connector is located under steering column.

what year? here's 2003 rear air only info, not 4 wheel air.

you have a fuse panel in truck and 1 under hood.




Visual Inspection Chart Mechanical Electrical

• Restricted suspension movement
• Excessive vehicle load
• Cut, severed or crimped air line(s)
• Unmounted height sensor
• Damaged air spring(s)

• Open fuses:
  • Central junction box (CJB) Fuse 4 (15A), 6 (5A) and 20 (5A)
  • Battery junction box (BJB) Fuse 109 (50A)
• Loose, corroded or disconnected connectors
• Air suspension switch is in the OFF position
• Damaged solenoid valve(s)

• compressor is inoperative

• BJB Fuse 109 (50A).
• Air compressor assembly.
• Circuitry.
• Air suspension relay.

• Go To Pinpoint Test P .

----------------------------------------------------------------------------

The system consists of unique rear air springs, the air compressor, air lines, air spring solenoids, height sensor, air suspension control module, attachments and associated signals derived from both driver and road inputs. With these components and signals, the air suspension control module commands changes in vehicle height that are necessary for the load leveling features.
The load leveling feature rear air suspension (RAS) systems shall automatically make adjustments in vehicle height so that the vehicle is always at trim height and constant front-to-rear vehicle attitudes are maintained over the expected load range of the vehicle. Adjustments in height that are necessary to correct height differences between the vehicle's left and right sides for the RAS system shall be restricted to what can be reliably achieved with one air suspension height sensor.
The system uses one air suspension height sensor, a steering sensor, generic electronic module (GEM) and other vehicle sensors to measure driver and road inputs. The system changes vehicle height using an air compressor, two air lines and the use of air springs with air spring solenoids.

Air Suspension Switch
The air suspension switch supplies power to the air suspension control module. Without the air suspension control module receiving this power, the load leveling system is inoperative and will not react when the rear of the vehicle is raised or lowered. If the air suspension system is disabled by turning off the air suspension switch, a "CHECK SUSP" will appear in the RH corner of the instrument cluster with the ignition in the run position.
Air Compressor
The RAS air compressor:

• consists of the compressor and vent solenoid; neither are replaceable as individual items.
• is a single cylinder electric motor driven unit that provides pressurized air as required.
• is powered by a solid state relay which is controlled by the air suspension control module.
• passes pressurized air through the compressor air drier that contains silica gel (a drying agent). Moisture is then removed from the compressor air drier when vented air passes out of the system during vent operation.
• air drier has a single port.
• air drier may be replaced separately.
• incorporates a snorkel that may be replaced separately.

The vent solenoid:

• allows air to escape from the system during venting actions.
• is part of the air compressor cylinder head.
• has a 1,103 kPa (160 psi) internal relief valve.
• shares a common electrical connector with the air compressor motor.
• is enclosed in the cylinder head casting, which forms an integral valve housing that allows the valve tip to enter the pressurized side of the system.
• has an O-ring seal that prevents air leakage past the valve tip.
• opens when the air suspension control module determines lowering is required.
• provides an escape route for pressurized air that opens when system pressures exceed safe operating levels.
• is replaced with the air compressor as a unit.

Air Spring
RAS vehicles use air springs in the rear. The air springs provide a varying spring rate proportional to the systems air pressure and volume. The air suspension system regulates the air pressure in each air spring by compressing and venting the system air. Increasing air pressure (compressing) raises the rear of the vehicle while decreasing air pressure (venting) lowers the rear of the vehicle. Vehicle height is maintained by the addition and removal of air in each air spring through an air spring solenoid installed in the upper spring cap and energized through the air suspension control module.
The two air springs support the conventional rear leaf coil springs.
Air Suspension Height Sensor
One air suspension height sensor is mounted on the vehicle. The air suspension height sensor sends a voltage signal to the air suspension control module. The output ranges from approximately 4.75 volts at minimum height (when the vehicle is low or in full jounce), to 0.25 volts at maximum height (when the vehicle is high or in full rebound). The air suspension height sensor has a useable range of 80 mm (3.2 in) compared to total suspension travel of 200-250 mm (8 to 10 in) at the wheel. Therefore, the air suspension height sensor is mounted to the suspension at a point where full rear suspension travel at the wheel is relative to 80 mm (3.2 in) of travel at the air suspension height sensor. The air suspension height sensor is attached between the No. 5 frame crossmember (upper socket) and the panhard rod (lower socket).
When the air suspension height sensor indicates that the rear of the vehicle is lower than trim under normal driving conditions, the air compressor will turn on and pump compressed air to the air springs. When the sensor indicates that the rear of the vehicle is raised above trim under normal driving conditions, this will cause the air to be vented from the air springs to lower the vehicle back to its trim height level.
Compressor Relay
The compressor relay is energized by the air suspension control module to allow high current to flow from the battery to the compressor motor.

• A solid state relay is used in the air suspension system for air compressor control. The relay incorporates a custom power metal oxide semi-conductor field effect transistor (MOSFET) and ceramic hybrid circuitry. The relay switches high current loads in response to low power signals and is controlled by the logic of the air suspension control module.

Air Suspension Control Module
NOTE: The 4WAS air suspension control module is used for the RAS system. The internal processor recognizes external circuitry to determine if it is installed in a 4WAS or a RAS equipped vehicle.
NOTE: The air suspension control module is calibrated with information from the air suspension height sensor. A new or exchanged air suspension control module requires a ride height adjustment calibration process to be performed.
The air suspension control module controls the air compressor motor (through a solid state relay), and the air spring solenoids. The air suspension control module also provides power to the air suspension height sensor. The air suspension control module controls vehicle height adjustments by monitoring the air suspension height sensor, vehicle speed, a steering sensor, acceleration input, the door ajar signal, transfer case signals, and the brake pedal position (BPP) switch. The air suspension control module also conducts all fail-safe and diagnostic strategies and contains self-test and communication software for testing the vehicle and related components.
The air suspension control module monitors and controls the air suspension system through a 32-pin two-way connector. The air suspension control module is keyed so that the air suspension control module cannot be plugged into an incorrect harness. There are two sides of the harness connection to the air suspension control module. Each is uniquely colored and keyed to prevent reversing the connections.
Solenoid Valve, Air Spring
WARNING: Never rotate an air spring solenoid valve to the release slot in the end cap fitting until all pressurized air has escaped from the spring to prevent damage or injury.
The air spring solenoid:

• allows air to enter and exit the air spring during leveling operations.
• is electrically operated and controlled by the air suspension control module.
• is only installed as a unit.