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.

Real Time Damping Description and Operation
The RTD system is bi-state real time damping system. The Electronic Suspension Control (ESC) 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 RTD system consists of the following:

• ESC Module
• Compressor/Leveling Module
• Air Pressure Sensor
• Exhaust Solenoid
• Compressor Motor Relay
• Steering Handwheel Speed/Position Sensor
• Electronic Variable Orifice (EVO) Solenoid
• Suspension Damper Solenoids
• Suspension Position Sensors

The objective of the ESC module is to provide ride and handling results that are superior to a passive damper system, both on and off road at all load conditions. The ESC module monitors body-to-wheel height, vehicle speed, handwheel position/speed, lift/dive status and a driver tow/haul input switch status in real time and instantly selects a "normal" or "firm" mode. This is done for each of the front and rear shock absorbers in order to adjust the vehicle for specific road and driving conditions.
The ESC 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 ESC module also uses the steering handwheel position/speed sensor and vehicle speed inputs to control a power steering effort control valve.
The suspension damper solenoid is driven ON and OFF by the ESC module. To activate the solenoid, it is initially subjected to full battery voltage for a short period of time. Once the solenoid is pulled-in, the supply voltage is Pulse Width Modulated (PWM) . The amount the suspension damper solenoid is activated is based on inputs from the driver Tow/Haul switch, road inputs, position sensor inputs and the PCM. The ESC module provides a common ground for all four of the suspension damper solenoids.
The ESC module provides a common regulated voltage of approximately 5 volts to all four of the body-to-wheel suspension position sensors, air pressure sensor and the steering handwheel position/speed sensor. The ESC module receives VSS discrete output from the PCM. The suspension position sensors provide an analog signal voltage between 0.5 and 4.5 volts to the ESC module. This signal voltage represents the wheel's position relative to the body. The ESC module provides a 5 volt reference and a low reference to the suspension position sensors.
Ignition cycle counting is used by the ESC module to detect faults in the system. The objective is to eliminate false/intermittent codes while maintaining an acceptable level of system performance. The operation of the ignition cycle counting requires that a fault condition be present for four consecutive ignition cycles before it will set the fault code and display the "SERVICE RIDE CONTROL" message. If a fault code is present (without a fault being current), the system will go into one or more degraded modes without displaying a message. Resetting the ignition cycle counter is done by clearing codes with a scan tool. Clearing codes will override ignition cycle counting for one ignition cycle. Therefore, a fault condition will set the fault code immediately if it occurs on the first ignition cycle after the codes are cleared.
There are two different ESC modules being used in the 02 MY. They have the same Z55 RPO, except that one also has and additional ZK3 RPO. The module with the additional ZK3 RPO connects to the EVO solenoid.
Programming procedures for the ESC modules is different. The ESC module with the RPO Z55 and RPO ZK3 can be programmed and have the ALC trimset performed with the use of the scan tool only. This is done by selecting Recalibration under SPECIAL FUNCTIONS on the scan tool and following the instructions displayed.
The ESC module with RPO Z55 only has to be programmed using the scan tool and the techline terminal. This is done by selecting Recalibration under SPECIAL FUNCTIONS on the scan tool and following the instructions displayed. In order to perform the ALC trimset, ALC Trimset has to be selected under SPECIAL FUNCTIONS on the scan tool and the instructions displayed followed.