The automatic level control (ALC) system maintains a desired rear suspension position under all types of towing, hauling and loading conditions. The following components are involved in the operation of the ALC system:
| • | Air line tubing--Pressurized air from the ALC compressor is pumped to each of the rear shocks via air line tubing. |
| • | Air drier--Pressurized air from the compressor is run through a drier containing a moisture absorbing chemical preventing water accumulation in the rear shocks. |
| • | Compressor--Supplies pressurized air to the rear shocks |
| • | Compressor motor relay--The relay supplies battery positive voltage to the ALC compressor motor. |
| • | Pressure sensor--The electronic suspension control module (ESCM) module provides a 5-volt reference and low reference to the ALC pressure sensor. The module receives the signal voltage that is relative to the air pressure applied to the rear
shocks. |
| • | ESCM--Controls the ALC system and electronic suspension control (ESC) system and detects failures in both. The module monitors inputs from the position sensors, and pressure sensor to determine when to raise and lower the vehicle to trim height
as the vehicle is loaded or unloaded. The module limits pump activation to 255 seconds to prevent thermal damage. |
| • | Exhaust valve--An electric solenoid activated by the ESCM to vent air pressure from the rear shocks. |
| • | Left and right rear suspension position sensors--The module provides a 5-volt reference and low reference to all 4 of the body-to-wheel suspension position sensors. The sensors send the ESCM a signal voltage that is relative to the rear suspension
ride height |
| • | Left and right rear shock absorbers with internal air chambers and dampers--Dampens the rear suspension and maintains trim height depending on the air pressure applied. |
Automatic Level Control (ALC) System Operation
The following are functions of the automatic level control (ALC) system:
Ride Height Increase
The ESCM detects a voltage signal from the rear suspension position sensors indicating the suspension height is low. The module grounds the control circuit of the compressor motor relay which in turn supplies battery voltage to the compressor. The exhaust
valve is open for 1.5 seconds during compressor pump start up in order to reduce current draw and pump motor wear. Air pressure from the compressor is pumped to the rear shocks through small flexible tubing. The increased pressure inside the rear shocks
raises the suspension to trim height.
Ride Height Decrease
The ESCM detects a voltage signal from the rear suspension position sensors indicating the suspension height is high. The module opens the exhaust valve by supplying ground. Air pressure from the rear shocks vent, lowering the suspension to trim height.
Self Pressure Test
Each time the ignition is turned ON the ESCM commands on the ALC relay, activating the compressor for 4 seconds. The ESCM then monitors the air pressure sensor's signal voltage to verify the compressor is functioning and the system is holding air
pressure.
