I have a 2006 Buick Rainier with a rear air suspension system. It used to stays up if the engine is on. It slowly goes down ( not all the way) if parked for several hours. Goes down "all the way" overnight. When started in the morning, the pump runs continuously for 30 to 60 seconds and levels the vehicle out. However, it is not going up anymore. My brother check to see if he could find a hole in the air bag and unconnected and then reconnected the pump. The truck pump back up for a day. Now it is completely down. Do I need to replace the pump? If so is it expensive. Please help