Many of the problems that arise in the Self- Leveling Systems(SLS)
are caused by leaks, so the main thing is to look for leaks.
Leveling Valve - This valve is located just in behind the rear axles and differential, slightly on the left side. The valve can leak internally; in this case you won't see fluid on the valve. It can also leak externally; visible moisture on the outside of the valve. If it is leaking please see our article on rebuilding your leveling valve
Accumulators - Diagnosing this isn't as easy, the accumulators have a rubber bladder in them, with suspension fluid on one side and gas on the other. They can get holes in the rubber and then the fluid gets into both sides and the accumulator fails. By poking the eraser end of a pencil into the accumulator you can feel around the diaphragm for a tear. The pencil should only go half way into the accumulator. If there is a tear in the diaphragm you'll be able to poke the pencil all the way in.
Struts - Struts aren't often the source of problems with the SLS, they rarely go bad. When they do, they usually start to leak; so look for suspension fluid on them (there shouldn't be any).
Pump - The pumps generally don't break, but they can start leaking. They usually leak internally and cause one of two things to happen. They allow engine oil to be introduced into the SLS system, or they allow the SLS fluid to go into the motor oil. If the SLS fluid in the reservoir is black it has motor oil in it, or its really old fluid. Either way it should be changed. If you keep losing fluid but it's not leaking anywhere else, then it is going into the motor. The pump is always creating pressure, which is just sent back to the reservoir when the car is in the neutral position. When the car is loaded the valve then sends the pressure to the accumulators and struts which expands the struts and causes the rear to lift until it hits the neutral position again. The other thing that can happen associated with the pumps are the hoses. There is one going from the reservoir to the pump and one going from the pump to the leveling valve. Make sure they aren't leaking. The one going to the valve is high pressure so if it gives out you'll have a big mess on your hands.