The control unit is equipped with a diagnostic program that will display trouble codes occurring in this trip and also store intermittent codes in a history file. As with any electronic system, GM stresses the importance of visual inspection. Even more sophisticated is the Lexus LS400 semi-active suspension, where the driver can select not only damping rate, but also spring rate and three different ride height positions for the whole car. Just below that motor is the air spring, consisting of upper and lower air chambers connected by an internal passage. Low, normal or high ride height is accomplished by changing the pressure in both chambers.
Spring rate is controlled with a valve in the passage between the air chambers.
When the valve is closed, there is less volume for the air to occupy during strut compression, effectively increasing the spring rate. The air lines from the compressor connect to the lower chamber and include one solenoid valve for each unit and a common vent valve for the whole system. The four height sensors are similar to the rotary type used on other cars, but the control unit also monitors road and driving conditions with acceleration sensors. One is mounted on each front height sensor and moves vertically with each front wheel. A third acceleration sensor is on the body in the rear.