2005 GMC Envoy Owner's Manual - Page 315

Electronically Controlled Air Suspension System Your vehicle may be equipped with an electronically controlled air suspension system that automatically keeps your vehicle level as you load and unload. The system includes a compressor, two height sensors and two air springs supporting the rear axle. The system also has an internal clock to prevent overheating. If the system overheats, all leveling function stops until the system cools down. During this time, the indicator light on the air inflator system will be flashing. The ignition has to be on for the system to inflate, in order to raise the vehicle to the standard ride height after loading. The system can lower the vehicle to the standard ride height after unloading with the ignition on and also for up to 30 minutes after the ignition has been turned off. You may hear the compressor operating when you load your vehicle, and periodically as the system adjusts the vehicle to the standard ride height. Load leveling will not function normally with the inflator hose attached to the inflator outlet. Remove the inflator hose from the outlet during loading and unloading. If the vehicle is parked for an extended period of time, some bleed down of the suspension is normal. Upon starting the vehicle, proper height will be achieved. Overload Protection The air suspension system is equipped with overload protection. Overload protection is designed to protect the air suspension system, and it is an indicator to the driver that the vehicle is overloaded. When the overload protection mode is on, it will not allow damage to the air compressor. However, do not overload the vehicle. See Loading Your Vehicle on page 4-43. If the suspension remains at a low height, the rear axle load has exceeded GAWR (Gross Axle Weight Rating). When the overload protection mode is activated, the compressor operates for about 30 seconds to one minute without raising the vehicle depending on the amount of overload. This will continue each time the ignition is turned on until the rear axle load is reduced below GAWR. 4-49