I have a 2004 Discovery with 104,000 miles. About two weeks ago, I got up and noticed the rear suspension was "low" on my truck. It had been about 36 hours since I last drove it. I started the truck and let it warm up for a couple of minutes and drove it around the block. The rear end lifted up back to its normal level.

It was fine until last weekend. Same issue. Hadn't driven it for a day and a half and the same issue. Started it up and took it for a quick spin to the end of the block and back and it again raised back up.

This hasn't happened before. What am I looking at? From what I've learned, the truck has air bags in the rear. There is a compressor or a pump, some hoses, a sensor and the air bags...? Can the problem be anywhere along that line? How can I debug it? Is this common? If so, where is the likely problem? Is it something that I can service? If I take it in, what should I expect to pay to have it repaired?

Thanks a lot for your help in advance!

spray soapy water on all of the bags just after driving it (with the suspension up) and look for leaks. I would hit the connections for the air lines too. Most common is a leaky bag. You can get a replacement at Arnott with a lifetime warranty, or you can convert to coils and disable the air suspension.

I don't have my Rave Manual handy...at the office. Are there instructions on bag replacement in the manual?

Yes. Not too tricky. I will add that I have heard about 50-50 on replacing the bags vs. the coil conversion. Personally, I would keep the bags for a better ride..

How many miles on the truck and are both sides dropping equally?

Mike:

The the truck has 104,000 miles. Yes, both sides are droping. I wwas reading the Arnott website. They indicated that the sensors hardly ever fail and if the compressor goes, it is likely related to faulty air spring (bag). Is it most likely that I'm going to find it is the bags...? Or potentially some other issue?

Do they drop equally? if they do, it is not air bags cause they are not tied together, it will be ECU related. Granted at you mileage your bags have to be brittle and porus, but I would check a little further before you buy the Arnott's which by the way are great bags.

It is almost always the air bags.
After it has sat and the rear is lowered start the truck and then shut the doors and stick your head under the passenger side and listen for the compressor.

I would dump the air ride and go with coils springs and you will never have suspension problems ever again.

Okay....changing to coil springs looks to be about the same cost and about the same effort.

I have to ask, what is the ECU? You mentioned if they both side dropped equally, it could be the ECU.

The ECU is the computer that controls the SLS.
Yes, you can switch to coils but the ride will be quite different and id you want to do the switch right, you will need front and rear springs and shocks or the truck will not sit level.