SUSPENSION CONTROL: AIR SUSPENSION SYSTEM (w/o AVS): SYSTEM DESCRIPTION (2008 Sequoia)

SYSTEM DESCRIPTION

1. REAR AIR SUSPENSION SYSTEM DESCRIPTION

This system uses pneumatic cylinders instead of the coil springs that are used in a conventional rear suspension. The suspension control ECU analyzes the information based on the switches, sensors, and input signals, operates the compressor assembly, and uses the solenoid valves to control the vehicle height.
The suspension control ECU detects, via the height control sensor, the changes in the rear vehicle height that results from the number of occupants or the amount of the load. Then, the suspension control ECU controls the height control solenoid valves and the compressor assembly in order to automatically adjust the rear vehicle height to a constant (normal) vehicle height.
Furthermore, three vehicle heights can be selected by operating the height control switch: HI, NORMAL, and LO. The HI vehicle height ensures performance on rough roads. The LO vehicle height facilitates the entry and exit of the occupants and the loading and unloading of cargo. The NORMAL vehicle height helps realize excellent controllability and riding comfort during normal driving.

2. FUNCTION OF MAIN COMPONENTS

Component	Function
Height Control Mode Select Switch	Used to select vehicle height control mode (Auto/Manual). Used to operate or stop auto leveling control.
Height Control Switch	Auto mode: Used to select vehicle height (HIGH, NORMAL, LOW). Manual mode: Used to select vehicle height optionally.
Height Control Sensor (LH, RH)	Converts the vertical change of the rear vehicle height, in proportion to the standard, to signals and detects vehicle height.
Height Control Indicator Light (Combination Meter)	Auto mode: Target vehicle height is displayed (HIGH, NORMAL, LOW). Manual mode: Current vehicle height is displayed (HIGH, NORMAL, LOW).
Height Control Manual Indicator Light (Combination Meter)	Comes on during manual mode. Blinks when the suspension control ECU detects a system malfunction. Blinks during test mode.
Pneumatic Cylinder Assembly (LH, RH)	Supports the vehicle body and adjusts the vehicle height.
Compressor/Height Control Dryer (No. 1 Height Control Compressor)	The compressor generates compressed air that is necessary to raise vehicle height and supplies it to the pneumatic cylinder assemblies. The dryer removes moisture from the compressed air.
Exhaust Solenoid Valve (No. 1 Height Control Compressor)	Discharges compressed air from the pneumatic cylinder assemblies to lower the vehicle.
Leveling Solenoid Valve (No. 2 Height Control Valve Sub-assembly)	Adjusts the air pressure in the pneumatic cylinder assemblies to raise or lower the vehicle height.
Gate Solenoid Valve (No. 2 Height Control Valve Sub-assembly)	Opens or closes the passage between the pneumatic cylinder assemblies LH and RH.
Suspension Control ECU	Estimates vehicle condition based on the signals from sensors and switches, and outputs the control signals to the compressor and valves. Blinks the height control manual indicator light when a system malfunction is detected.
Air Suspension Relay (AIR SUS)	Supplies electricity to the compressor motor.
Main Body ECU	Receives the signals of the door courtesy light switches, and sends them to the suspension control ECU through CAN communication.
ECM	Sends the engine speed signal and shift position signal to the suspension control ECU through CAN communication.
Skid Control ECU	Receives the signals of the stop light switch and speed sensors, and sends them to the suspension control ECU through CAN communication.