Mailbag: 1998 Cadillac Eldorado suspension compressor not working

[Bruce Nunnally]

Rameke wrote on Google+:

How are you? I hope all is well. Im having some issues with my 98 Eldorado and Im having a hard time find some answers. The compressor for the suspension is not working. Ive check the fuse in the trunk and even adjusted the sensor behind the LR tire. Any suggestions?

Do you know if the compressor is getting power?

To be honest I have no idea where it is. I'm new the the Cadillac world

I have opened a thread in the forum on this topic for you. http://caddyinfo.ipbhost.com/index.php?showtopic=43809 I don't have a 98 shop manual but I am looking to see if the same issue in my 96 shop manual what help it has

Ok thank you so much... I found the car at a really good deal... 39k miles... $1500. No issues accept for the suppension ....

that system I believe is called Electronic Level Control. Have you run the codes on the onboard diagnostics?

Yes...

Give me a few I'll get them to you

Did you get any current codes that relate to ELC?

Not that I can tell...

Sdm b1160

B1159

U1255

B1327

The rest are under msm

I did get one under mmm

Not sure what category that is

Mmm b1983

[Bruce Nunnally]

ok big picture is that the rear is not self-levelling? When you put luggage in the rear is sitting too low?

I was told if the battery was weak the compressor would not work... Any truth to that.. it's time for me to replace it... It's at least 5 years old and I had to get a jump today

My truck is empty and it's sitting low

Trunk...

Let's talk about how the system works for a second. The compressor is an air compressor. When the level lever is in the right position, it signals the compressor to pump air into the shocks in the rear in order to raise the car

For the system to work, the lever has to move properly, the solenoid it switches has to work properly, the compressor has to have power, the compressor has to work properly, and the air from the compressor has to be piped to the struts, and the struts have to not leak. Does that all make sense?

Yes sir

so to tell what is not working, you have to check each one of those to see if they are true or not.

Ok. I'll get on that. Thanks for your time and info

The compressor looks like a typical air compressor. if you don't HEAR the compressor coming on after you turn on the car -- it may have a delay -- then that is part of the problem. If the compressor is coming on, but the air tubes from the compressor to the strut are not there or leaking, that would be the problem. Could be multiple problems oddly enough

The system is not very well understood by most casual mechanics as it doesn't come up that much but is pretty simple.

It sounded like you checked the obvious item, which is is the level lever working right, and not out of alignment somehow. Not clear if we know what the 'right' setting is though? I recall a write-up on the forum that described it well.

I think what happens sometimes is you get a leak, then the compressor runs a LOT, to try to keep up, and burns out. But dont' throw in a new compressor until you make sure that it is getting power when it should be getting power and not coming on.

That's why i'm building the forum post from our conversation though is some of the other readers know more about the ELC and may have better suggestions.

Ok. That sounds great. Thank you so much

[Cadillac Jim]

B1159 Loss of Serial Data-Key Not Received
U1255 Class 2 Communication Malfunction (Serial Data Line Malfunction)
B1327 Vehicle system voltage below 9.0 volts

MMM (memory mirrors module)
B1983 Device Power Circuit Low

I was told if the battery was weak the compressor would not work...

(Bruce was more tactful, "The system is not very well understood by most casual mechanics....")

You do have two codes that indicate that the battery is low: B1327 and B1983. These codes are usually thrown when the battery voltage drops below 9.0 Volts when you start the car. Check the connections on the battery cables and clean them first and see if that doesn't solve your problem. If it doesn't and if an overnight trickle charge doesn't put the battery back in shape, you need a new battery. But that is likely separate from the automatic leveling system problem.

The compressor runs for a few seconds when you first turn on the key. This is when the car's computers test the ALC. The system maintains about 7 psi in the rear shocks for an empty car to keep the car level. It stays on for about 5 minutes after the key is turned off.

I have a 1997 factory shop manual (FSM) and will use that here. In 1998, the Seville had a platform change but the Eldorado never changed platforms after 1992, although there were upgrades in suspension and other systems. I believe that the 1997-1999 Eldorados were almost identical except for feature changes.

I believe that your car has the RSS feature, which is electronically controlled shocks and struts. If there is an RSS category when you run your codes, you have RSS. If you do not have RSS, there are differences in the ELC schematic and I need to know to correct any schematic information.

On page 3D1-3 of the FSM, in the section for ELC for cars with RSS, it shows that there is a 10 Amp fuse that powers the compressor in the trunk compartment fuse block labeled IGN-0 BODY that is hot with the key in Run position. It powers the coil of a relay in the trunk compartment #2 relay center labeled ELC or RELAY "A". It is operated by the CVRSS module by grounding one of the relay coil terminals. If you do not have RSS the relay coil is grounded by a separate ELC Height Sensor package that is not labeled a module but is integrated with the height sensors in the rear.

The compressor (and exhaust solenoid, which lets the system down when it is too high) is powered through a 30 Amp MAXI CIRCUIT BREAKER that has power at all times. An ORN wire goes from it to the relay and to the solenoid. A DK GRN wire goes from the relay to the compressor motor. The ground for the system is G403 on the LR Seat Back.

The FSM says to service any CVRSS codes before starting diagnosis. Pay particular attention to codes labeled CURRENT regardless of what throws those codes.

The air compressor, vent solenoid, and drier/filter assembly are mounted in a bracket mountin in the body rail in the underbody above the right rear crossmember.

You haven't described what is happening that causes you (or the previous owner) to believe that there is a problem with the ELC. If the compressor isn't coming on, or if the system has a leak, the rear will ride too low. If the vent solenoid doesn't work or is clogged, the rear will ride too high. If you have neither problem, your ELC is probably working OK.