Circuit/System Description
The automatic level control (ALC) module performs checks of internal calibration data. If a fault condition is detected, the ALC module will set the fault DTC, and may, depending upon the fault type, turn ON the SERVICE SUSPENSION SYSTEM message. Recovery from any controller fault condition is attempted only after the ignition is cycled ON and OFF.
The automatic level control (ALC) position sensor provides a signal voltage between 0.5-4.85 volts to the ALC module. This signal voltage represents the wheel's position relative to the body. The ALC module provides a 5-volt reference and a low reference to the sensor.
The electronic suspension control (ESC) module provides a common regulated reference voltage of approximately 5 volts to all of the position sensors. The ESC module monitors this power supply for a malfunction that could prevent it from correctly regulating the supply voltage.
The electronic suspension control module (ESCM) adjusts the vehicle suspension ride height. The ESCM determines the height of the vehicle based on the voltage from the suspension position sensors. The module grounds the ELC relay and the exhaust control solenoid to raise and lower the vehicle in order to keep the vehicle level.
The automatic level control (ALC) System uses the electronic suspension control module (ESCM), level sensors, compressor, and exhaust valve to increase or decrease air pressure in the system to control trim height. Battery voltage is supplied to the exhaust valve and compressor relay. The ESCM controls the ground circuits that activate the exhaust valve and compressor relay which maintain trim height based on the level sensor input voltage.
The automatic level control (ALC) System uses the electronic suspension control module (ESCM), level sensors, compressor, and exhaust valve to increase or decrease air pressure in the system to control trim height. Battery voltage is supplied to the exhaust valve and compressor relay. The ESCM controls the ground circuits that activate the exhaust valve and compressor relay which maintain trim height based on the level sensor input voltage.
Automatic Level Control Description and Operation
The automatic level control (ALC) system maintains a desired suspension position under all types of towing, hauling, and loading conditions.
The system uses the electronic suspension control module (ESCM), ELC relay, ALC compressor assembly, air dryer, air lines, shock absorbers with integral air chambers, suspension position sensors, exhaust valve, driver information center (DIC), and the serial data circuit to perform the system functions.
When the vehicle is unloaded, the suspension is at a desired position, which is monitored by the ESCM using the position sensor signal voltage inputs. As weight is added to the vehicle, the position sensor signal voltage inputs change. When the ESCM detects a steady substantial change in the position sensor signal voltages for at least 10 seconds, it responds by commanding ON the ELC relay, which activates the compressor causing the air pressure in the shock absorber chambers to inflate. This inflation raises the vehicle to regain the desired suspension position. When weight is removed from the vehicle, the ESCM responds by commanding ON the exhaust valve causing the air pressure in the shock absorber chambers to deflate. This deflation lowers the vehicle to regain the desired suspension position.
The compressor is a positive displacement piston air pump driven by a 12-volt DC permanent magnet motor. The compressor draws filtered air through an intake line attached to an under body rail. The compressed air is then run through a dryer containing a moisture-absorbing chemical that dries the compressed air before it is sent to the shock absorber chambers. Each time the compressor is activated, the ESCM commands ON the exhaust valve for 1.5 seconds to release air from the compression chamber in the compressor's cylinder head ensuring low motor current draw upon compressor activation. The ESCM also limits the amount of compressor run time to 255 seconds to protect the compressor components from thermal damage.
The system also performs a self test on each ignition ON cycle in which the ESCM commands the ELC relay ON, activating the compressor for 4 seconds then monitors the position sensor signal voltage inputs to verify the compressor is functioning and the system is holding air pressure.
The ESCM has the ability to detect malfunctions within the ALC system. Any malfunctions detected will cause the DIC to display the SERVICE SUSPENSION SYSTEM message. For more information on other functions of the ESCM, refer to Electronic Suspension Control Description and Operation .