05 STS level control diagnosis

Wiring, DIY, lighting, etc.
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: General STS thread

Post by kevm14 »

Adam helped fashion up a compressor bracket and we spent several hours trying to make it solid and long lasting. Only, the compressor doesn't run. I don't think it is getting power, based on connecting my DVM to the harness after starting the car. I should have seen 12V from the test cycle.

Maybe there is another issue. Though the old compressor DID run and did NOT make air, so that was definitely broken.

Naturally I don't have any pics of the finished product as it was getting late.
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kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: General STS thread

Post by kevm14 »

Sitting in the dentist office...

I wonder if the plug I put on the car side dragged on the muffler and shorted a fuse or something. I will have to check the fuses. I will also probably jumper the relay when I get in there and make some basic determination about the wiring and such.
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: General STS thread

Post by kevm14 »

Plot gets thicker.

Finally got the rear seat bottom cushion off which required much struggling (but no tools) and sweat dripping everywhere. The fuse looks good. I jumped the compressor motor pins of the relay plug and....it ran! Not only did it run but it brought the rear of the car up. So that is all working.

So I thought, maybe the relay is bad. I swapped in the rear defroster relay which is the same. Still nothing. Then I put my DVM on the relay solenoid pins and started the car. I should see 12V for the relay coil and I saw like....0.3V and then it dropped to zero. So something is going on.
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Time to consult the FSM.
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: General STS thread

Post by kevm14 »

I didn't exactly follow the FSM procedure but did my own detective work with the schematic information that it provided.

Here are the things I did:
- Jumper motor control pins of the relay receptacle. Motor ran and rose car. Good.
- Swap relays to test the relay. Used a known good relay in the ALC slot. Did not work.
- DVM relay coil pins when I expected the compressor to run. Saw like 0.3V at most and then 0V. Not good.
- Unplugged Electronic Suspension Control harness at module in trunk. Harness has two pins of note. Pin 6, shorted to ground, grounds the other pin at the relay coil wire in the fuse box. After starting the car, this DID run the motor.
- The other pin of interest, pin 20, does the same thing but with the exhaust solenoid on the compressor. This also worked.

The last two are very telling. What it means is the entire system after the ESC module seems to be working properly, including the fuses, relays and wiring, and the compressor, air lines and shocks. What it also means is the ESC module does not seem to be commanding the compressor to run when it is supposed to (after ignition run). So either there is some logic that I don't understand...which to try to fix that, I disconnected the battery cables and touched them together to potentially reset things. Or, the ESC module itself is somehow malfunctioning.

What I really need at this point is a good Tech 2 (or aftermarket equivalent). I can trigger the compressor and relay via the ESC, and at least determine if the ESC is able to do so. I would also need the Tech 2 if I replaced the ESC module, to do some kind of initialization programming (ride height stuff, and maybe VIN code, etc.).

I think one of those tools would be a good investment and there are some good options under $500. Right now I will probably put the car back together and just drive it, hoping something will wake up and start working. Probably unrealistic.

ESC module.
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kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: General STS thread

Post by kevm14 »

So there are two DTCs for the ALC system.

One checks the motor control circuitry and the other checks the exhaust solenoid control circuitry. Failures of both tests should result in a message of "SERVICE SUSPENSION SYSTEM" and a limit of 80 mph. And I'd have DTC C0712 or C0660. I don't have either.

So...now this makes zero sense. The one thing I seem to have narrowed the problem down to has internal diagnostic capability. And I'm getting no errors there.

Could really use that Tech 2...
Attachments
2005 STS DTC C0712.pdf
(21.33 KiB) Downloaded 74 times
2005 STS DTC C0660.pdf
(22.6 KiB) Downloaded 85 times
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: General STS thread

Post by kevm14 »

kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: General STS thread

Post by kevm14 »

Some light reading.

I need to look closely at how those two DTCs could trigger. Specifically, I want to know if it simply monitors the grounding of the two control pins on the ESC (which is done locally within the unit) or if it is somehow looking for some voltage which it would see when it makes the connection to the relay and exhaust solenoid. If it is the former, then I think a broken wire near the ESC harness could be the issue. If it is the latter, then I think I am having some kind of ESC problem internally.
Attachments
2005 STS Automatic Level Control Description and Operation.pdf
(20.41 KiB) Downloaded 31 times
2005 STS Automatic Level Control schematic.pdf
(116.33 KiB) Downloaded 34 times
2005 STS DTC C0660.pdf
(22.6 KiB) Downloaded 34 times
2005 STS DTC C0712.pdf
(21.33 KiB) Downloaded 36 times
2005 STS ESC connector end view.pdf
(207.41 KiB) Downloaded 95 times
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: General STS thread

Post by kevm14 »

This is from an 09 FSM:
The automatic level control (ALC) system maintains a desired suspension position under all types of towing,
hauling, and loading conditions.
The system uses the electronic suspension control module (ESCM), ELC relay, ALC compressor assembly, air
dryer, air lines, shock absorbers with integral air chambers, suspension position sensors, exhaust valve, driver
information center (DIC), and the serial data circuit to perform the system functions.
When the vehicle is unloaded, the suspension is at a desired position, which is monitored by the ESCM using
the position sensor signal voltage inputs. As weight is added to the vehicle, the position sensor signal voltage
inputs change. When the ESCM detects a steady substantial change in the position sensor signal voltages for at
least 10 seconds, it responds by commanding ON the ELC relay, which activates the compressor causing the air
pressure in the shock absorber chambers to inflate. This inflation raises the vehicle to regain the desired
suspension position. When weight is removed from the vehicle, the ESCM responds by commanding ON the
exhaust valve causing the air pressure in the shock absorber chambers to deflate. This deflation lowers the
vehicle to regain the desired suspension position.
The compressor is a positive displacement piston air pump driven by a 12-volt DC permanent magnet motor.
The compressor draws filtered air through an intake line attached to an under body rail. The compressed air is
then run through a dryer containing a moisture-absorbing chemical that dries the compressed air before it is sent
to the shock absorber chambers. Each time the compressor is activated, the ESCM commands ON the exhaust
valve for 1.5 seconds to release air from the compression chamber in the compressor's cylinder head ensuring
low motor current draw upon compressor activation. The ESCM also limits the amount of compressor run time
to 255 seconds to protect the compressor components from thermal damage.
The system also performs a self test on each ignition ON cycle in which the ESCM commands the ELC relay
ON, activating the compressor for 4 seconds then monitors the position sensor
So look at that. On the 09, it activates the ALC and looks for a change in height. Simple. Why doesn't the 05 do this then if it's that simple? They couldn't figure this out in 05? I do think the MR system had some kind of generational change after 06 as I think the shock and ESC compatibility changes. Maybe they made it smarter.
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: General STS thread

Post by kevm14 »

Sharing this post I found at the Cadillac Forums.
BOSE AMP PROBLEM Solved. No sound from stereo, door chimes etc. 2006 STS
Yep, mine went out. After studying the BOSE Surround System in the STS 1SF, I realized how fast tech becomes obsolete, especially in lux cars. I gambled and bought a pre owned AMP off EBAY plugged it in and WALA!

BUT.. The Gamble? there is no test for the out of the head unit, So I have no Idea if I just fed an AMP to a hungry monster.
The AMP wiring harness is beyond crazy thick.
The AMP controls way too many gadgets in the car.

A couple years ago, it seemed the bluetooth volume and reception was kicking out. Right before the AMP failed, There was a loose noise, sound coming from the front driver's side tweeter.


I've owned the STS for a decade. Not too many problems, but when it has them, I'm like WTF? who designed that? Like the Power Steering line that blew out.

Best upgrade was getting rid of the low profile sport tires, and getting some rubber around those rims..(adding height and width) filling up the wheel wells and smoothing the bumps in the road.
It seems like he did not need a Tech 2 as part of that amp replacement, which is encouraging.
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: General STS thread

Post by kevm14 »

kevm14 wrote:I didn't exactly follow the FSM procedure but did my own detective work with the schematic information that it provided.

Here are the things I did:
- Jumper motor control pins of the relay receptacle. Motor ran and rose car. Good.
- Swap relays to test the relay. Used a known good relay in the ALC slot. Did not work.
- DVM relay coil pins when I expected the compressor to run. Saw like 0.3V at most and then 0V. Not good.
- Unplugged Electronic Suspension Control harness at module in trunk. Harness has two pins of note. Pin 6, shorted to ground, grounds the other pin at the relay coil wire in the fuse box. After starting the car, this DID run the motor.
- The other pin of interest, pin 20, does the same thing but with the exhaust solenoid on the compressor. This also worked.

The last two are very telling. What it means is the entire system after the ESC module seems to be working properly, including the fuses, relays and wiring, and the compressor, air lines and shocks. What it also means is the ESC module does not seem to be commanding the compressor to run when it is supposed to (after ignition run). So either there is some logic that I don't understand...which to try to fix that, I disconnected the battery cables and touched them together to potentially reset things. Or, the ESC module itself is somehow malfunctioning.

What I really need at this point is a good Tech 2 (or aftermarket equivalent). I can trigger the compressor and relay via the ESC, and at least determine if the ESC is able to do so. I would also need the Tech 2 if I replaced the ESC module, to do some kind of initialization programming (ride height stuff, and maybe VIN code, etc.).
Took it apart again. Blew out the sunroof drain.

I unbolted the ESCM and fooled around with it and the harness and it didn't help. I also found an alligator clip and a small pin instrument which made testing even easier. Compressor and exhaust solenoid run every time and stay running. I guess this is an ESCM problem. I still think I will need a Tech 2 to initialize the new (or used) ESCM and if I had a Tech 2, I could further diagnose my ESCM.
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