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Automatic leveling quits working while driving


hjb981

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The rear leveling on my '97 DeVille is acting up. If I drive the car with no people in the back, it is usually fine. It levels and stays leveled. If I put some stuff in the trunk (like during a recent road trip vacation), the car stays level for maybe 20 - 60 minutes (it varies) and then sinks down in the back. This is very noticeable during night driving, since I can see on the reach of the head lights if the leveling changes.

I am 100% sure that I had not overloaded the car during the road trip - just some clothes and stuff, and there where no people riding in the back seat. Actually, the same thing will happen if there are people in the back seat, but nothing in the trunk.

I have tried putting stuff in the trunk and standing on the edge of the open trunk while the car is leveling, and it levels ok (even though it takes a while, but I am unsure how long it is supposed to take). So it seems that it is able to level, but for some reason stops after a while.

If I have people in the back seat, and the car stops leveling, it will be very noticeably sunk down on the back wheels even after they exit the vehicle. Turning off the ignition and then back on again restarts the leveling system, whether the load is still in the car or not.

There are no codes.

What is going on? What should I check?

How likely do you find the following?

-bad air compressor

-leaky air cusions

-bad coil springs (thus putting to much load on the leveling system)

I have a feeling that the system shuts itself off due to overload (due to some faulty component), but should it not set a code then?

Some general information on how that system works would also be appreciated, more specifically: where are the leveling air bags located?

Leveling%2097%20DeVille.jpg

The image shows a back wheel of the car car after driving with passengers in the rear seat, and as comparison after the car was switched off an on to make the leveling system work again. Look at the difference in the distance between the top of the rim and the sheet metal above it.

Any tips on how to diagnose and fix this would be greatly appreciated!

Best regards,

Jonas

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Be sure that you are getting all the codes. Most inexpensive aftermarket code readers will see only PCM codes that affect emissions.

If indeed you are getting no codes, the only thing that I can think of are the position sensors on the rear. If one of them has a bent or missing link, it might upset the leveling without the PZM setting a DTC. That doesn't explain why you can make it work by turning the key off and then back on, though.

A more likely problem would be a bad connection in a fuse terminal. Look at the fuses in the trunk compartment fuse block and see if there is corrosion on the fuse terminals.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Thanks, I will check the fuses. I use the climate control cluster when I check for codes (no external code reader), and it cycles through body codes as well as some other stuff, so I think that I can see them all. In other words, I am pretty sure that there are no codes.

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Yes, there is no substitute for the climate control interface on a Cadillac for reading OBD codes, other than a Tech II or a $400+ aftermarket reader.

There is a 30 Amp circuit breaker in the Maxifuse block. It powers both the compressor motor and the exhaust vent solenoid. In my FSM, this circuit diagram is on page 8A-42-4 and 8A-42-5. If it's tripping but the ELC works anyway, perhaps the circuit breaker itself is bad. There is also an ELC relay in the trunk compartment relay center that switches power to the compressor on command from the CVRSS module that may be going bad. If those don't do it, you may be looking at a compressor/valve assembly.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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hope this helps, I have seen a common problem with the compressors on the mid 90s models that has to do with excessive moisture buildup in the compressor due to the exhaust valve not exhausting. (because the exhaust valve corrodes internally ) and cannot exhaust properly thus holding moisture in the compressor which shorts the compressor or overloads the compressor.

I believe if you had a leak the best way to find out is to leave the car overnight and see if the rear end sags in the morning.

Also check the compressor ground cable as they also corrode and create alot of heat therefore losing connection

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Thanks for the input! The car does sag most of the times if I leave it overnight.

New question: is it normal that the car sags if it is not loaded with almost anything in the trunk, even if the air cushions do leak? Shouldn't just the coil springs be enough to keep the car at normal height when it is not loaded? Or is it supposed to sag even unloaded if there was no pressure in the air cushions?

Where can I find information on how this system works, like e.g. where the air cushions are located? I don't have a factory service manual yet.

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The rear shocks need to have 14 psi to 28 psi in them to keep the car level, even if unloaded, according to the FSM.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Issues like this is when I wish the car had an light on the dash to let the driver know when the compressor was running / the car was leveling.

My Fleetwood Brougham has a green LEVEL RIDE light on the instrument panel that comes on when the compressor is running. For some reason, that was eliminated after the '94 model year and I don't think it was included on the FWD Devilles.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Your rear shocks have the air lift inc. to the shock absorber body itself...

Thank you, now I got a little more of the basics :).

The rear shocks need to have 14 psi to 28 psi in them to keep the car level, even if unloaded, according to the FSM.

That is very useful information - I guess that means that I should not be overly worried about something being wrong with the coil springs then.

Issues like this is when I wish the car had an light on the dash to let the driver know when the compressor was running / the car was leveling.

My Fleetwood Brougham has a green LEVEL RIDE light on the instrument panel that comes on when the compressor is running. For some reason, that was eliminated after the '94 model year and I don't think it was included on the FWD Devilles.

My '88 DeVille (FWD) also had that light. With my '97, I can of course check it when the car is standing still (since it is then audible), and it is very obvious that it is not running when I stop after driving for a while with passengers, even though the back is sagging (like in the left image). As soon as the ignition is switched off and on, it levels (as in the right image).

Leveling%2097%20DeVille.jpg

Btw, this morning the car was not sagging at all, even though it had been sitting since the evening of the day before yesterday. When I leave it with some stuff in the back, it sags after a few hours (as was the case on my resent road trip). Maybe something leaks above a certain pressure...

Which would be the possible leak points, and how do I check them?

Thanks! :)

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I will take a guess that there may be a leak, and the compressor shuts down (as not to overheat). BUT I would think this would set a code. I am away from my FSM to see if there is a troubleshooting session for this. - again, not sure if thru the DIC (Off&Warmer) there is a way to set the overrides, and check the imputs for the leveling system. (As there are for almost every other system).

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I will take a guess that there may be a leak, and the compressor shuts down (as not to overheat). BUT I would think this would set a code. I am away from my FSM to see if there is a troubleshooting session for this. - again, not sure if thru the DIC (Off&Warmer) there is a way to set the overrides, and check the imputs for the leveling system. (As there are for almost every other system).

I remember that light. It was cool. I also really miss the telescoping steering column from the 80s.

The springs are not enough to hold the car up without the air shocks.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I will take a guess that there may be a leak, and the compressor shuts down (as not to overheat). BUT I would think this would set a code. I am away from my FSM to see if there is a troubleshooting session for this. - again, not sure if thru the DIC (Off&Warmer) there is a way to set the overrides, and check the imputs for the leveling system. (As there are for almost every other system).

That was exactly what I thought also: leak -> compressor shutdown, but why no code? If you or anyone else can find the troubleshooting chart for this, that would be very helpful for me.

I remember that light. It was cool. I also really miss the telescoping steering column from the 80s.

The springs are not enough to hold the car up without the air shocks.

And I miss the fiber optics that showed if the lights were working. Very nice to see turn signals and high beams without having to look at the dashboard. :)

I will be going to Las Vegas this fall - guess I will try to buy a FSM then... Should be more useful than the Chilton and Haynes DIY manuals I have now. But for now I don't have it, so the flowchart for troubleshooting would certainly help me.

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