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[AAS]

My Elite 2.2DTi estate has self-levelling shocks on the rear. Over the last few days I have just noticed that the rear of the car is extremely jacked-up and equal on both sides. Although this doesn't seem to have effected the steering etc. it does look daft and cannot be right. I have a long journey to undertake (Leeds from London) with a partial load and I'm concerned about safety.

I noted that the shocks are original GMs (self-levellers only available from GM apparently) and were fitted about 10,000 miles /15 months ago. No sign of leaking. They have a small air-pipe feeding the top of both. With the engine off when I pull-off one pipe there is a loud hiss, and over a period of 5-10 secs. the rear suspension lowers equally on both sides and reverts to normal sitting position. I have not carried any heavy loads ever, and the car had been sitting for about two weeks.

My local 'guru' mechanic who fitted the new shocks is at a loss although he muttered something about a height sensing mechanism, and sent main to the main dealer. He suggested 'a sticky valve in one/other shock' and £400 to replace them which I fear may not solve the problem. It looks to me that the shocks are being incorrectly commanded to pump-up, and to me this looks like a weight/height sensor issue.

I reconnected the air pipe and drove for about 10 miles. When I stopped, I checked and the suspension had pumped up (equally) again. Pull off the air pipe and it reset.

Can anyone cast any light on this specifically ....

1) heard of this before?
2) is it likely to be a sensor issue?
3) what is that sensor - electrical? pneumatic? mechanical?
4) where is it
5) can it be over-ridden at least temporarily and safely?
6) or do you think it really is one or other shock?
7) where does the air supply come from?

I much appreciate your input. Thank you,

Alan
Sussex

[TheBoy]

Physically check the sensor is still attached (near diff, on suspension arm).

[AAS]

Thanks. What am I looking for? Is it electrical with wires or mechanical with tubes or whatever? Thanks. Alan

[feeutfo]

See the guide sections.

[RobG]

Thanks. What am I looking for? Is it electrical with wires or mechanical with tubes or whatever? Thanks. Alan

http://www.omegaowners.com/forum/YaBB.pl?num=1250308202

[Andy H]

Maintenance Guide Index

Test/Raise self levelling suspension

What the guide doesn't say is that the most likely cause is the sensor arm becoming disconnected but it could be due to a faulty sensor or frayed wiring.

I don't know which fuse you would need to pull but I imagine it would be safe to disable the compressor until you fix it.

[AAS]

That's most helpful - thank you.

What I'm still not completely clear about please ... is the signal to apply air an electrical one? In other words, is there some motion-to-electrical activity in that sensor box near the rear? I ask because if that is the case then it may be possible to fault-find be taking an electrical reading from the sensor, or at least a continuity check. If it's entirely mechanical/pneumatic then that's beyond my ability. Thanks again.

[feeutfo]

Fuse 27 but will also disable the rear aux socket. Or unplug the pump in drivers front wing.

[feeutfo]

Or one of the relays in the cabin fuse box.

[Andy H]

That's most helpful - thank you.

What I'm still not completely clear about please ... is the signal to apply air an electrical one? In other words, is there some motion-to-electrical activity in that sensor box near the rear? I ask because if that is the case then it may be possible to fault-find be taking an electrical reading from the sensor, or at least a continuity check. If it's entirely mechanical/pneumatic then that's beyond my ability. Thanks again.

I may be wrong but I think the pneumatics are limited to
- 2 dampers
- 1 air compressor
- a piece of pipe from the compressor to a tee piece and 2 pipes to the dampers.

The compressor housing also houses a valve to let the air out when necessary.

The sensor measures the rear ride height (electrically) and somewhere there is a bit of electrickery that averages out that information and decides whether to run the pump or open the valve. I'm guessing that it is in the compressor housing because that allows the wiring to the sensor to be kept simple.

Don't worry to much about the finer detail until you have looked to see if the sensor is still connected (physically and electrically).

[belldarr]

Alan - I had the very same thing happen to my saloon elite, it turned out to be a broken spring on the drivers side, it had snapped near the top and was quite difficult to see without the car being up on a lift but this somehow affected the sensor to pump more air into the shocks - worth having a good look at both rear springs.

Darren

[AAS]

Again this is really most useful info. I appreciate all the comments. Proves what a wonderful forum this is.

[AAS]

OK I have been under the car and here is my report. I reset the suspension by pulling-off one air line to the rear shock as before.


1) The springs look OK but a break could indeed be concealed and I need an expert to really check this with good lighting

2) Thanks to the aforementioned guide, I found the sensor mechanism. It was securely attached and as I rocked the car up and down the rt. angle lever arm seemed to move accordingly (hence reflects the car's rear height).

3) I found that one end of the arm could be disconnected (it was in a ball joint) leaving the sensor arm (pressed tin) able to freely move.

4) With the ignition off, handbrake on, I prized off the rod from the ball joint and pushed the 90deg. pressed tin lever arm upwards. This would simulate heavy load, and a call for compressed air to be supplied to the shocks.

5). Started engine: over a minute or two the rear shocks equally pumped-up and held that position as expected.

6) (I think the engine was still running) I reached under car with a long screwdriver and pushed the tin arm downwards (meaning light load) expecting the rear suspension to drop (on me). Nothing happened.

7) Ignition off. Remove air line from shock, suspension reset. Refitted ball joint so level arm in normal position with zero load. Load is zero, car empty.

Restated ignition. No obvious pumping-up. Observed for 5 minutes.

9) Located fuse 27, removed it.

10) Drove for 10 miles. Stopped. Checked suspension. Seemed normal (as expected with no power to suspension pump). Handling etc. normal.

So it seems that for some reason with fuse 27 in, the suspension will (incorrectly) pump-up under zero load, but won't vent the air when the load is removed.


As I see it there can be three possible faults:

A) Either shock absorber (unlikely)
b) Sensor mechanism not sending a 'deflate shocks' command and erroneously sensing an 'inflate shocks' command under zero load (as I found when first detected this problem in normal driving)
c) fault in the compressor (behind headlight) whereby it misinterprets sensor command and/or has a vent-to-air fault.

Any thoughts please? Thanks again. Alan

[Broomies Mate]

Do we know the frequency in which the system checks the 'load'?  Is it done with every turn of the key, or every 10 seconds/5 minutes etc etc?

[feeutfo]

It's not unusual for the pump to fail to vent air. But this usually means the pump increases ride hight over a longer period of time.

How long does it take for the ride to become excessive? If ten minutes I would suspect sensor fault as the pump must be continually running , you should be able to hear it in the cabin over the engine. If a couple of days or several engine starts I would suspect pump not releasing air due to the system setting itself on each start up. It will run the pump to a level it senses to be too high then release to the correct hight. Hence the longer period to over fill the shocks with air.

The engine does not need to be running for sl to activate, but if run too long it will flatten the battery. But you should be able to hear the pump run with engine on and release air with engine off.

Hth.