What does air suspension consist of - 2006 GMC Envoy XL Denali

Why do you want to change the BCM ? What problems are you having ? Your best bet , have a qualified technician hook up a scanner an read code's .Your vehicle doesn't even have a BCM .
Module Controlled Functions The multifunction modules consist of the following:

• air suspension module
• driver door module (DDM)
• lighting control module (LCM)

The air suspension module is linked to its own data link connector (DLC). The air suspension module controls the air suspension system and the electronic variable orifice (EVO) steering.
The DDM is connected to the international standards organization (ISO) 9141 communication network. The DDM controls many functions including power door locks and remote keyless entry (RKE).
The LCM is connected to the ISO 9141 communication network. The LCM controls both interior and exterior lighting, backlighting, the battery saver and warning chimes.

Do yourself a favor an take it to a qualified repair shop.

Air Suspension ??????

Air Suspension Description and Operation
Air Suspension
The primary mission of the Air Suspension System is the following for the rear suspension under loaded and unloaded conditions:
• Keep the vehicle visually level
• Provide optimal headlight aiming
• Maintain optimal ride height
The Air Suspension System consists of the following items:
• Air suspension compressor assembly
• Air suspension sensors
• Rear air springs
Important: The Air Suspension System must have a voltage supply of at least 12.6V to operate properly.
The Air Suspension System will maintain the rear D height within 4 mm (0.15 in) in all loading conditions and the leveling function will deactivate if the vehicle is overloaded. The side to side D height variation is maintained within 8 mm (0.31 in). After ignition is turned off, the air suspension control module (ASCM) will remain active for between 30 minutes and 2 1/2 hours. The system will exhaust pressure within 30 minutes after the ignition is turned off to lower the vehicle after unloading. In a temperature-controlled environment, the leakage of the complete load leveling system will not result in more than 1.4 mm (0.05 in) drop of rear suspension height at GVWR during a 24 hour period. If the outdoor temperature drops from +20°C (+68°F) to -5°C (+23°F), the rear D height may drop as much as 25 mm (1 in). However, the Air Suspension System should return to the specified D height when the ignition is again cycled to ON.

What is the problem ?

Diagnostic Trouble Code (DTC) Displaying
The Air Suspension system has an internal clock to prevent overheating if the compressor assembly is running for a prolonged period of time. If the system overheats, all leveling function stops until the system cools down. During this time, the indicator LED on the air inflator switch will be quickly flashing at a constant rate.
The other three diagnostic trouble codes are displayed with a blink code on the inflator switch LED. The Air Suspension Compressor Assembly shall begin to indicate the code when the condition to cause the code becomes current.
The number of the fault code shall be represented by the number of flashing pulses on the inflator switch LED. The flashing pulses shall have a repetition rate of 0.5 seconds and each code shall be separated by a 3.0 second delay. All codes shall be flashed in the order of occurrence of the fault. The blink code shall take priority over other processes that have access to the inflator switch LED. Refer to the following:
• DTC 001
• DTC 002
• DTC 003

Trim Height Uneven or Low ??????

Having it hooked up to a factory scan tool would be your best bet . Check for DTC'S diagnostic trouble codes . Without testing ,code scan ,we'd only be guessing .
Very complex , the untrained person hasn't got a pray of fixing this . You have no idea what your dealing with . Vehicle Dynamic Suspension The vehicle dynamic suspension consists of the following components:

• Rear air suspension control (RAS) module (5A919)
• Snorkel
• Drier
• Air compressor (5319)
• Air suspension switch (5K761)
• Solenoid valve (5311)
• Air spring (5560)
• Air suspension height sensor (5359)
• Air line
• Rear Air Suspension Control Module
  A microprocessor controls the air suspension system. The microprocessor and its supporting hardware are contained in the rear air suspension control module. The rear air suspension control module responds to signals from various sensors in the vehicle to maintain the programmed ride height while the vehicle is either moving or stopped. The rear air suspension control module accomplishes this by opening and closing solenoid valves to control the amount of air in the air spring(s). The rear air suspension control module turns on the compressor by applying voltage through the compressor relay to inflate the air spring(s) and raise the vehicle. The rear air suspension control module opens the vent solenoid to lower the vehicle by releasing air from the air spring(s) in response to signal inputs from the air suspension height sensor(s).
• Rear Air Suspension Control Module Diagnostic Trouble Code (DTC) Index DTC Description Source Action B1317 Battery Voltage High Rear Air Suspension Control Module GO to Pinpoint Test C . B1318 Battery Voltage Low Rear Air Suspension Control Module GO to Pinpoint Test C . B1342 ECU Is Defective Rear Air Suspension Control Module INSTALL a new rear air suspension control module. REFER to Module-Air Suspension Control . TEST the system for normal operation. C1441 Steering Sensor Channel A Circuit Failure Rear Air Suspension Control Module REFER to Section 211-00 . C1442 Steering Sensor Channel B Circuit Failure Rear Air Suspension Control Module REFER to Section 211-00 . C1722 Air Suspension Height Sensor Power Circuit Short to Power Rear Air Suspension Control Module GO to Pinpoint Test D . C1723 Air Suspension Height Sensor Power Circuit Short to Ground Rear Air Suspension Control Module GO to Pinpoint Test E . C1760 Air Suspension Rear Height Sensor High Signal Circuit Failure Rear Air Suspension Control Module GO to Pinpoint Test F . C1763 Air Suspension Rear Height Sensor High Signal Circuit Short to Ground Rear Air Suspension Control Module GO to Pinpoint Test G . C1765 Air Suspension Rear Height Sensor Low Signal Circuit Failure Rear Air Suspension Control Module GO to Pinpoint Test F . C1768 Air Suspension Rear Height Sensor Low Signal Circuit Short to Ground Rear Air Suspension Control Module GO to Pinpoint Test H . C1770 Air Suspension Vent Solenoid Output Circuit Failure Rear Air Suspension Control Module GO to Pinpoint Test I . C1773 Air Suspension Vent Solenoid Output Circuit Short to Ground Rear Air Suspension Control Module GO to Pinpoint Test J . C1790 Air Suspension LR Air Spring Solenoid Output Circuit Failure Rear Air Suspension Control Module GO to Pinpoint Test K . C1793 Air Suspension LR Air Spring Solenoid Output Circuit Short to Ground Rear Air Suspension Control Module GO to Pinpoint Test L . C1795 Air Suspension RR Air Spring Solenoid Output Circuit Failure Rear Air Suspension Control Module GO to Pinpoint Test M . C1798 Air Suspension RR Air Spring Solenoid Output Circuit Short to Ground Rear Air Suspension Control Module GO to Pinpoint Test N . C1813 Air Suspension Vent Request Exceeded Max Timing Rear Air Suspension Control Module GO to Pinpoint Test O . C1818 Air Suspension Air Compressor Request Exceeded Max Timing Rear Air Suspension Control Module GO to Pinpoint Test P . C1830 Air Compressor Relay Circuit Failure Rear Air Suspension Control Module GO to Pinpoint Test Q . C1832 Air Compressor Relay Circuit Short to Power Rear Air Suspension Control Module GO to Pinpoint Test R . C1840 Air Suspension Switch Circuit Failure Rear Air Suspension Control Module GO to Pinpoint Test S . C1842 Air Suspension Switch Circuit Short to Power Rear Air Suspension Control Module GO to Pinpoint Test D . C1897 Steering VAPS Circuit Loop Failure Rear Air Suspension Control Module REFER to Section 211-00 . U1041 SPC Invalid or Missing Data for Vehicle Speed

Hi Jose:
The first place to start is to have Ride Control Module scanned for trouble codes, this requires a high end scan tool. Most common problem is the air compressor in the rear or a height sensor. Here is how the system works.

Automatic Level Control Description and Operation
The RTD system is bi-state real time damping system. The Suspension Control module controls the suspension damper solenoids and suspension position sensors, along with parts of the automatic level control (ALC) system and electronic variable orifice (EVO) power steering system.

The Automatic Level Control system consists of the following:
• Suspension Control Module
• Compressor/Leveling Module
- Air Pressure Sensor
- Exhaust Solenoid
• Compressor Motor Relay

The objective of the Automatic Level Control System is to provide constant ride height at all load conditions. The Suspension Control module monitors body-to-wheel height, and vehicle speed.

The Suspension Control module will use the rear body-to-wheel displacements and vehicle speed inputs to keep the rear trim height of the vehicle at its desired level.

The electronic suspension control (ESC) system is bi-state real time damping system. The ESC module controls the suspension damper solenoids and suspension position sensors, along with parts of the automatic level control (ALC) system, if 1500 series.

The ESC system consists of the following:
• The ESC module
• The compressor/leveling module, if 1500 series
- The air pressure sensor, if 1500 series
- The exhaust solenoid, if 1500 series
• The compressor motor relay, if 1500 series
• The steering handwheel speed/position sensor
• The suspension damper solenoids
• The suspension position sensors

Hope this helps; also keep in mind that your feedback is important and I'll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using Fixya, and have a nice day.

SERVICE A - CONSIST OF BRAKE SYSTEM INSPECT AND SERVICE.ENGINE + OIL FILTER CHANGED. EXTERIOR LAMPS INSPECT AND SERVICE.FAULT CODES.READ CLEAR.FLUID LEVELS TOPPED OFF.SERVICE INDICATOR LIGHT RESET.STEERING AND SUSPENSION INSPECT AND SERVICE.TIRE AIR PRESSURE INSPECT AND ADJUST.WINDSHIELD WIPERS REPLACED.

I will check the shop manual, but the module does control ride for stiffness, increased stiffness at higher speeds, etc. If the bags are inflated, then the module cintrols how much air to allow in or out based on inputs to the module. See if you can get one from a salvage yard form a cash for clunkers car.

A dealer can run a test for fault codes in the computer. Call and ask how much for just a scan for fault codes in the air suspension module.

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Vehicle Dynamic Suspension The vehicle dynamic suspension consists of the following components:

• Rear air suspension control (RAS) module (5A919)
• Snorkel
• Drier
• Air compressor (5319)
• Air suspension switch (5K761)
• Solenoid valve (5311)
• Air spring (5560)
• Air suspension height sensor (5359)
• Air line

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Rear Air Suspension Control Module
A microprocessor controls the air suspension system. The microprocessor and its supporting hardware are contained in the rear air suspension control module. The rear air suspension control module responds to signals from various sensors in the vehicle to maintain the programmed ride height while the vehicle is either moving or stopped. The rear air suspension control module accomplishes this by opening and closing solenoid valves to control the amount of air in the air spring(s). The rear air suspension control module turns on the compressor by applying voltage through the compressor relay to inflate the air spring(s) and raise the vehicle. The rear air suspension control module opens the vent solenoid to lower the vehicle by releasing air from the air spring(s) in response to signal inputs from the air suspension height sensor(s).
Air Suspension Switch
CAUTION: The air suspension switch must be turned to the OFF position when the vehicle is hoisted, jacked, towed, jump started, or raised off the ground, to avoid unnecessary operation of the system and possible damage to the air suspension system components.
The air suspension switch provides a signal to the rear air suspension control module in the ON position to activate the system to maintain the programmed vehicle height.
Air Compressor
NOTE: The compressor contains a thermal overload circuit breaker. The circuit breaker automatically resets after a cool down period and after being tripped by excessive compressor motor heat.
The air compressor assembly consists of the compressor pump, electric motor and vent solenoid (must be installed as an assembly).
Air Suspension Height Sensor
The air suspension height sensor sends signals to the air suspension control module. There are three possible conditions that the air suspension control module interprets from the signals of the air suspension height sensors. The conditions are trim height, below trim height, or above trim height.
Solenoid Valve, Air Spring
WARNING: Never rotate an air spring solenoid valve to the release slot in the air spring end cap fitting until all pressurized air has escaped from the air spring to prevent vehicle damage or personal injury.
The air spring solenoid valve allows air to enter and exit the rear air springs during height adjustment operations. The air spring solenoid valve is electrically operated and controlled by the air suspension control module.
Steering Sensor
The steering sensor provides the steering rate and position to the air suspension control module to avoid overcompensation of the air suspension during turns.
Inspection and Verification

1. Verify the customer concern.

1. NOTE: If the door ajar indicator is illuminated, repair the door ajar indicator. For additional information, refer to Section 413-09 .
   Visually inspect for obvious signs of mechanical and electrical damage.

Visual Inspection Chart Mechanical Electrical

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

• Central junction box (CJB) Fuse:
  • 8 (10A)
  • 17 (10A)
• Battery junction box (BJB) Fuse 12 (30A)
• Loose or corroded connectors
• Air suspension switch
• Damaged air spring solenoid(s)

1. If the concern remains after the inspection, connect New Generation STAR (NGS) Tester to the data link connector (DLC) located beneath the instrument panel and select the vehicle to be tested from the NGS Tester menu. If NGS Tester does not communicate with the vehicle:
   • check that the program card is properly installed.
   • check the connections to the vehicle.
   • check the ignition switch position.

1. If the NGS still does not communicate with the vehicle, refer to the New Generation STAR Tester manual.

1. Carry out the DATA LINK DIAGNOSTIC TEST. If NGS Tester responds with:
   • CKT914, CKT915 or CKT70 = ALL ECUS NO RESP/NOT EQUIP. Refer to Section 418-00 .
   • NO RESP/NOT EQUIP for rear air suspension control module, go to Pinpoint Test A.
   • SYSTEM PASSED, retrieve and record the continuous diagnostic trouble codes (DTCs), erase the continuous DTCs and perform self-test diagnostics for the rear air suspension control module.

1. If the DTCs retrieved are related to the concern, go to Rear Air Suspension Control Module Diagnostic Trouble Code (DTC) Index to continue diagnostics.

1. If no DTCs related to the concern are retrieved, proceed to Symptom Chart to continue diagnostics.

Rear Air Suspension Control Module Diagnostic Trouble Code (DTC) Index
NOTE: If rear air suspension control module C251 is disconnected before rear air suspension control module C250, DTCs C1830, C1770, C1790 and C1795 will be retrieved and must be cleared before an accurate list of continuous DTCs can be retrieved. The DTCs C1441 and C1442 will only be retrieved when running the electronic variable orifice (EVO) functional test on NGS Tester. The DTC C1897 will only be retrieved once per ignition switch cycle.

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Module —Air Suspension Control Removal
WARNING: Before performing maintenance on any air suspension components, disconnect the power to the system by turning off the air suspension switch located on the LH side of the luggage compartment to prevent vehicle damage or personal injury.
CAUTION: Electronic modules are sensitive to static electrical charges. If exposed to these charges, damage may result.

1. Turn the air suspension switch off.

1. Disconnect the battery ground cable (14301).

1. Pull out the lower instrument panel insulator.
   1. Remove the pushpins.
   1. Pull out the lower instrument panel insulator.

1. Remove the lower instrument panel insulator.
   1. Disconnect the power point.
   1. Disconnect the courtesy lamp.
   1. Remove the lower instrument panel insulator.

1. Remove the rear air suspension control module.
   1. Remove the screws.
   1. Disconnect the electrical connectors.
   1. Remove the rear air suspension control module.

Installation

1. NOTE: When the battery is disconnected and reconnected, some abnormal drive symptoms may occur while the vehicle relearns its adaptive strategy. The vehicle may need to be driven 16 km (10 mi) or more to relearn the strategy.
   To install, reverse the removal procedure.

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.

Vehicle Dynamic Suspension The vehicle dynamic suspension consists of the following components:

• Rear air suspension control (RAS) module (5A919)
• Snorkel
• Drier
• Air compressor (5319)
• Air suspension switch (5K761)
• Solenoid valve (5311)
• Air spring (5560)
• Air suspension height sensor (5359)
• Air line

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Visual Inspection Chart Mechanical Electrical

• Restricted suspension movement
• Excessive vehicle load
• Cut, severed, or crimped air line(s)
• Damaged air spring(s)
• Height sensor damage
• Height sensor mounted incorrectly, disconnected, or damaged

• Central junction box (CJB):
  • Fuse 5 (15A)
• Battery junction box (BJB):
  • Fuse 8 (30A)
• Loose or corroded connectors
• Air suspension switch OFF

The air suspension control module is diagnosed using Super Star II Tester 418-F045 (007-0041B) or equivalent.
The test connector used to communicate with the air suspension control module is located on the RH side of the luggage compartment.
When the tester is connected, the engine is started and the HOLD/TEST button is latched down, the air suspension control module will respond sending a code 10 to the Super Star II Tester which represents "Diagnostics mode entered." If diagnostic trouble code (DTC) 10 is not displayed, go to Pinpoint Test A.
Air Suspension Control Module Diagnostic Trouble Code (DTC) Index
Condition Possible Sources Action

• No communication with the air suspension control module

• CJB Fuse 5 (15A).
• BJB Fuse 8 (30A).
• Circuitry.
• Air suspension control module.

• GO to Pinpoint Test A .

• Unable to enter auto test

• Air suspension control module.
• Circuitry.

• GO to Pinpoint Test B .

• Rear air suspension does not respond to load changes

• Circuitry.
• Air compressor.
• Air compressor inlet tube.
• Air compressor drier.
• Air suspension height sensor.
• Air suspension control module.

• GO to Pinpoint Test C .

• Rear rides low/high

• Circuitry.
• Air spring solenoid.
• Air suspension height sensor.
• Air suspension control module.

• GO to Pinpoint Test C .

• Poor ride quality

• Circuitry.
• Air springs.

• GO to Pinpoint Test C .

• Air suspension warning indicator ON

• Air suspension switch OFF.

• Place the air suspension switch in the ON position.

• Air suspension control module.
• Circuitry.

• GO to Auto Test.

• Instrument cluster (conventional cluster) or lamp warning module (electronic cluster).

• REFER to Section 413-01A (conventional cluster) or REFER to Section 413-01B (electronic cluster), or REFER to Section 413-01C (natural gas cluster).

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 .

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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.

you need to check your real axle sensor it may have come loose or broken