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clusco said:
What exactly does this code above mean on my 1999 STS and how do I fix it?
Clusco - This code means that the Electronic Level Control is not working. There are two main parts to the ELC system, an air pump and a solenoid exhaust valve. The code is telling you that the exhaust valve is busticated. On my car, it was rusted out inside and not working. The ELC fuse would pop instantly after replacing it. Yours is probably popped right now.

On a 96 SLS, the pump and exhaust valve are located above the rear axle on the passenger side. Just follow the plastic air lines that come from the rear shocks. They end up at the pump/valve. It's moderately easy to change it out, but the replacement parts can be expensive. Last time I checked, www.gmpartsdirect.com wanted about $400-$500 for the whole setup. I have tried to find the exhaust solenoid by itself but so far have been unable to find it as a separate part, even though it looks like it could be replaced separately. It is sold as the pump/solenoid together. There is also a separate air dryer can attached to the pump, and I was told by a trustworthy mechanic that it's good to replace that can as well even though it's an additional expense. It will save your solenoid from getting rusty again. It's also a good idea to disconnect the air lines from the shocks and blow them out with air so you know for sure they're dry. While you're doing that, check them for leaks. If there are any leaks, that's where the water is getting in the system and the lines should also be replaced. Our old friend Rob said that it was best to just replace the plastic air lines at the same time, but I'm too cheap and lazy to do that. They checked out fine on my car and they've been working for 2.5 years now so I think checking them is the better policy.

I was able to find a used pump/solenoid at a salvage yard for $100. It came from an Olds Aurora, and it's the exact same pump but with a different mounting bracket. I just swapped the bracket from my car with the new pump and it fit perfectly for much lower cost.

Let me know what you find and if you have any questions. I've been through this same problem before, so I'll help any way I can.
 

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Discussion Starter #3
I talked to a mechanic at the local Cadillac dealership here in town and he told me that it is purely an electrical issue if that particular code comes up.

Mcowden, are you saying that the solenoid could be bad but to replace it you must replace the entire pump?
 

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clusco said:
I talked to a mechanic at the local Cadillac dealership here in town and he told me that it is purely an electrical issue if that particular code comes up.

Mcowden, are you saying that the solenoid could be bad but to replace it you must replace the entire pump?
The mechanic is right - it is an electrical issue, as indicated by the code description. Congratulations to him for having the ability to read. Unfortunately he didn't give you anything useful beyond that apparently. The electrical issue in my case was that the solenoid was badly rusted internally and that's where the short was, hence the electrical issue. It's possible that there could be a short elsewhere, so while you're down there, carefully inspect the wiring for frayed spots and bare copper that could be shorting out. My guess is you'll find the wiring to be just fine and the solenoid will be badly corroded and rusting internally.

I have heard before that there is a way to replace just the solenoid, but I couldn't figure out how to do that when I had mine apart. They are a single unit from what I can tell, so my only choice was to replace the pump at the same time even though it was working fine and only the exhaust valve solenoid was hosed. When I looked for replacement parts, I could only find the pump/solenoid assembly and still have never found just the solenoid for replacement. I'm not saying it's not out there or it's not possible, but while I was researching it, I never found the solenoid by itself. The salvage yard unit for $100 had everything I needed, so I just replaced all of it instead of fiddling around with dismantling the unit.

Maybe someone else will chime in with a description of how to remove just the solenoid or where to find one. Since you have to take the whole pump/solenoid unit down to replace either one or both anyway, I think I'd rather just replace the whole thing and eliminate the possibility that the pump was also damaged by water.
 

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Discussion Starter #5
What exactly is the pump's technical name...What should I ask for at the auto store or junk yard?
 

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What exactly is the purpose of this electronic level control and how long can I go before changing it out?
 

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clusco said:
What exactly is the purpose of this electronic level control and how long can I go before changing it out?
You don't have to change it out at all if you don't want to. The purpose of the thing is to determine the level of the rear of the car by the position of the suspension and bring the car to a standard height by raising or lowering the pressure in the rear air shocks. If you don't fix it, the rear of the car will not self-level. I don't know if it affects anything else or not. If you just unplug the compressor the code might go away. I don't know about that, though because I've never tried it.
 

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That raises an interesting point for my situation......
I just bought this 1999 STS last week and the code hadn't come up before. Previously I owned a 1995 STS and when I bought this newer STS I switched the "factory" rims from the '95 to the '99.

After I switched the rims, periodically the message, "SERVICE STABILITY SYSTEM", will come up from time to time. Could my switching the rims have affected this C1738 code to come up, perhaps a different offset?

And if so, is there an idle learn procedure to perform to make the '99 "get familiar with the dimensions of the its new rims' offset?

One last thing............ The SERVICE STABILITY SYSTEM message came up a lot when I first changed the rims out and now it hasn't come up in about 7 or 8 drives on the road.
 

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clusco said:
That raises an interesting point for my situation......
I just bought this 1999 STS last week and the code hadn't come up before. Previously I owned a 1995 STS and when I bought this newer STS I switched the "factory" rims from the '95 to the '99.

After I switched the rims, periodically the message, "SERVICE STABILITY SYSTEM", will come up from time to time. Could my switching the rims have affected this C1738 code to come up, perhaps a different offset?

And if so, is there an idle learn procedure to perform to make the '99 "get familiar with the dimensions of the its new rims' offset?

One last thing............ The SERVICE STABILITY SYSTEM message came up a lot when I first changed the rims out and now it hasn't come up in about 7 or 8 drives on the road.
The rims have nothing to do with the code directly, but it's possible one of the air lines was dislodged or damaged when you were working in there. If that happened, it could have let water into the system and contributed to the solenoid problem, but that would take a while to happen. If the code started soon after you replaced rims, I would say it's an unrelated event. The offset has nothing to do with this. It's an electrical problem, plain and simple, as the dealership mechanic already informed you so helpfully. The way to resolve it is to follow the steps I outlined above.

The idle learn procedure has nothing to do with the size of your tires either. That's only for things that would change the amount of air getting to the engine at idle or a new sensor or something engine-related. I think what you're talking about is the speedometer ratio. If the diameter of the tire changed substantially, you might need to have that adjusted, but I don't know how that's done. If you post that question as a new thread, you'll probably get the answer from someone who knows about that kind of thing.

The Service Stability System message would be caused by a code. If there are no codes besides the C1738, then either that code is setting the message (likely) or there is another problem and the code for it is already cleared. If it comes up again, check the codes right away and let us know.
 

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I just went through this last week with mine. 99STS, same code etc. I noticed for a few days that my compressor was running for a long time after start up and the car was not leveling. I went under the car and found one of my air bags on the rear shocks were leaking so I unplugged the 30 amp fuse under the back seat to shut the compressor off. It didn’t seem too bad until I priced them at $600.00.....EACH. But I had to have them, couldn't live with an STS with passive struts so I replaced them.
The sting had not even worn off when I got the code C1738. The struts pumped up great but would not come down at all. Every engine start cycle, when it test ran for a few seconds, would pump it a little higher without re-leveling. Not having the time to do any thing right away, I had to pull one of the hoses on one of the struts to release the air to level the car again and pull the fuse again.
The fun started when I had to drop the exhaust system to remove the compressor assembly. Luckily they have a flexible section in the exhaust pipe which let me lower it enough without disconnecting it.
The compressor ran fine but when I applied 12VDC to the solenoid no click...frozen. I pulled the head plate off, like 6 or 7 5/16" screws, and the solenoid was corroded and full of water from running continuously with the leaking air bag. The dryer was also full of water and probably the air lines.
The solenoid is not sold as a single part but the head assembly which includes the dryer is ( part # 12494810) for around $150.00. That’s if you can find one. My Florida parts guy couldn’t find one…anywhere in the country… and the $500.00 complete pump assembly which included the dryer was three days away ( part # 12494809).
I had to take an old solenoid out of an old Delco pump, cut the wires to the dead Cadillac one and use stake on connectors to connect the new(old) one.
The original Cadillac pump was sealed much better and directly wired to the solenoid. The older version, at least 12 years old, had the spade type connections which I had to bend over to clear the heat shield. I had to use the old head plate because the newerCadillac head plate had a different opening for the solenoid connection. Even after all these years the pumps were basically the same. I had to silicone the solenoid electrical penetration through the head plate to seal it better and it worked great… for now. I KNOW this exposed connection is not going to last very long but hopefully long enough to locate the head assembly.
One important thing about removing a good solenoid from an old head. Pry it straight away from its air connection. It has a little nipple on it with an O ring which fits into a hole in the side of the head. If you try to pry it “up” the nipple will break and… Oh Well…what was that junk yards phone number again?
I blew the dryer out with dry nitrogen until no more moisture came out, blew out the air lines, replaced the rubber air lines and tee fitting at the compressor which turned to dust when I touched them and re-installed the whole thing. Code gone. Car level.
Sorry for the long winded story. I hope it helps .
 

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Privateer said:
I just went through this last week with mine. 99STS, same code etc. I noticed for a few days that my compressor was running for a long time after start up and the car was not leveling. I went under the car and found one of my air bags on the rear shocks were leaking so I unplugged the 30 amp fuse under the back seat to shut the compressor off. It didn’t seem too bad until I priced them at $600.00.....EACH. But I had to have them, couldn't live with an STS with passive struts so I replaced them.
The sting had not even worn off when I got the code C1738. The struts pumped up great but would not come down at all. Every engine start cycle, when it test ran for a few seconds, would pump it a little higher without re-leveling. Not having the time to do any thing right away, I had to pull one of the hoses on one of the struts to release the air to level the car again and pull the fuse again.
The fun started when I had to drop the exhaust system to remove the compressor assembly. Luckily they have a flexible section in the exhaust pipe which let me lower it enough without disconnecting it.
The compressor ran fine but when I applied 12VDC to the solenoid no click...frozen. I pulled the head plate off, like 6 or 7 5/16" screws, and the solenoid was corroded and full of water from running continuously with the leaking air bag. The dryer was also full of water and probably the air lines.
The solenoid is not sold as a single part but the head assembly which includes the dryer is ( part # 12494810) for around $150.00. That’s if you can find one. My Florida parts guy couldn’t find one…anywhere in the country… and the $500.00 complete pump assembly which included the dryer was three days away ( part # 12494809).
I had to take an old solenoid out of an old Delco pump, cut the wires to the dead Cadillac one and use stake on connectors to connect the new(old) one.
The original Cadillac pump was sealed much better and directly wired to the solenoid. The older version, at least 12 years old, had the spade type connections which I had to bend over to clear the heat shield. I had to use the old head plate because the newerCadillac head plate had a different opening for the solenoid connection. Even after all these years the pumps were basically the same. I had to silicone the solenoid electrical penetration through the head plate to seal it better and it worked great… for now. I KNOW this exposed connection is not going to last very long but hopefully long enough to locate the head assembly.
One important thing about removing a good solenoid from an old head. Pry it straight away from its air connection. It has a little nipple on it with an O ring which fits into a hole in the side of the head. If you try to pry it “up” the nipple will break and… Oh Well…what was that junk yards phone number again?
I blew the dryer out with dry nitrogen until no more moisture came out, blew out the air lines, replaced the rubber air lines and tee fitting at the compressor which turned to dust when I touched them and re-installed the whole thing. Code gone. Car level.
Sorry for the long winded story. I hope it helps .
Wow! That's excellent information, Privateer, thank you very much for posting all of that. The ELC compressors and solenoids do go bad, and this question comes up from time to time. Your post will help someone down the line. Good work on the solenoid replacement! :thumbsup:
 

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Discussion Starter #14
Wow! That is a lot of information and it makes it clear to me that there is no way in the world I can accomplish this job by myself. Where would I get my hands on dry nitrogen? Man, if I bring this problem to the dealership, I am going to get gang raped though.

And I take it, this part, can't be bought at your local Autozone, etc...?
 

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Okay, for the code that I have acquired on me '99 STS, I understand that my exhaust solenoid has gone bad BUT to replace this part, you must change the entire compressor?

So if this is the case, I'd like to know how serious of a problem this is. If the solenoid is bad, does this mean that the compressor is not working at all or simply that the solenoid isn't sending a signal to my computer? The "SERVICE STABILITY SYSTEM" message only comes on every so often. For instance if I start up the car and drive down the road the message may appear if I swerve or slam on the brakes but if THEN at other times the message won't appear at all during a drive. So my question is: Is the car's ELC functioning properly before the message comes up on the display panel?

Lastly, if I do have to change the compressor set-up, is it relatively easy DIY job?

I know I typed a great deal here but any help is much appreciated and desperately needed. Thanks!
 

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clusco said:
Okay, for the code that I have acquired on me '99 STS, I understand that my exhaust solenoid has gone bad BUT to replace this part, you must change the entire compressor?

So if this is the case, I'd like to know how serious of a problem this is. If the solenoid is bad, does this mean that the compressor is not working at all or simply that the solenoid isn't sending a signal to my computer? The "SERVICE STABILITY SYSTEM" message only comes on every so often. For instance if I start up the car and drive down the road the message may appear if I swerve or slam on the brakes but if THEN at other times the message won't appear at all during a drive. So my question is: Is the car's ELC functioning properly before the message comes up on the display panel?

Lastly, if I do have to change the compressor set-up, is it relatively easy DIY job?

I know I typed a great deal here but any help is much appreciated and desperately needed. Thanks!
If the solenoid is shorted, the ELC fuse is probably blown. In that case, the compressor will not run. The ELC depends on correct functioning of the compressor and the solenoid. If one or the other fails, the entire system is useless. Check the ELC fuse and let us know. On my '96 it's in the fuse panel behind the rear seats, accessed by removing the carpet behind the seats in the trunk. I'm not sure where the fuse is on your car, though.

Changing out the compressor is a DIY job, I would say moderate skill level and no unusual tools. Privateer's message above is outstanding information. You can get away with just blowing the air lines out with air if you want, but nitrogen is better. I didn't do anything at all to mine.
 

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Discussion Starter #18
Ranger said:
Fuse block on the '99 is under the rear seat cushion.

Ranger,
When you say that it's under the rear seat cushion does that mean I have to access it by removing the rear seat or that I have to get to it from the trunk area?
 

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Lift up on the rear seat cushion. Unplug the heater connection on the passenger side, then remove the seat cushion. You'll find the battery and fuse block under there. No need to enter the trunk. The fuse block has a black cover on it with a red clamp.
 

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Discussion Starter #20
I just want to clarify something before we move any further:

Does the SERVICE STABILITY SYSTEM" message that randomly displays itself on my information panel every so often during drives have anything at all to do with the DIC code, "C1738"?

This morning I went out and checked under the back seat and looked at the ELC fuse (30 Amp) and it was good. Shouldn't that fuse be blown if the compressor was malfunctioning?
 
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