A while back the 2000 STS with F45 started showing a "service suspension system" display on the DIC intermittently, now it's on all the time and the rear end of the car is riding very low. I don't hear the ELC compressor running at all. Checked for current codes, this is what I have:
Driver Door Module
DDM B1982 Device Power Circuit High
Road Suspension System
RSS C0690 Damper Control Relay Circuit Malfunction
RSS C0896 Electronic Suspension Control (ESC) voltage is outside the
normal range of 9 to 15.5 volts

I located and swapped the damper relay with a known good relay, no change. I checked all the fuses under the back seat and they're good.
I'm having no luck finding more specific diagnosis info or wiring diagrams. I really don't want to drop the exhaust system until I know what to look for.
Guess I'm going to have to break down and get a GM shop manual.

Any constructive advice welcome,
k

The compressor/drier assembly is up in the right rear wheel well area, inboard of the well liner. The compressor should run for 4 seconds shortly after key: start. If not, then it's toast. Several threads in Seville and Deville over the last winter. $400+ for whole unit. Needs a lift and an afternoon, but not technical. You'll probably find a bunch of rusty water that runs out of the compressor lines. Cross your fingers that the rear ($$$$$$) shocks aren't ruined.

You really need to go back and search for a while: there's a lot of info about the replacement.

Roger that! I have read everything I could find here and elsewhere, but have not come across exactly the same symptoms. This afternoon I did some more hands on testing of the wiring to and from the relay and what you say pretty much confirms what I have concluded. Again, I sure didn’t want to drop the exhaust to get to the pump unless I had to. My tools have gotten a little rusty, but I should be able to handle it. Thanks!

I just looked at the FSM, and it appears that, although a PITA, you could disconnect the air lines at each rear strut/shock and blow back through them while the compressor is out. A healthy slug of air would get rid of any nasties in that part of the system, at least.

Thanks Sub. I ordered a new compressor/dryer assembly last week and installed it today. It's still not working. I hooked the old assembly up to 12V and it worked fine. Is there a relay someplace other than the damper relay that is in the fuse box under the back seat? I have already tried swapping that one out with a known good one. Still no 12V at the compressor.

The battery started going dead overnight from a 3 amp draw. I tracked it down to a module behind the rear seat, accessed from the trunk. Turns out it is the suspension control module. $800 at the dealer, $50 at the salvage yard. Everything is working now.