C5 X7 Rear Suspension Fault

[DHallworth]

Our recently acquired 3.0 HDi Exclusive (Saloon) has a strange fault with its rear suspension.

If you drop the suspension to it's lowest setting and then press the button to return it to normal height, the front will go to normal height but the rear suspension will stay on the floor. If you then press the "Up" button again, the front and rear will both raise to the intermediate height.

Pressing the down button will then drop the car to it's normal ride height and it'll sit there perfectly level.

When you unlock the car or open a door it'll level the front and rear with no problems, the problem only seems to happen when the car is dropped to its lowest setting.

When I initially scanned the CSS ECU on the car I got the following:

C1184 - Reference heights not programmed
C1195 - Front axle average movement
C1196 - Rear axle average movement
U2003 - Main wake-up
P0562 - Under voltage

The car has been sitting around for 3 or 4 months so the voltage faults are to be expected. I've cleared all the faults off it and the only one that's come back is "C1184 - Reference heights not programmed".

There is a receipt in the service history for a rear height sensor being replaced. I'm wondering if something has gone wrong whilst they've been trying to set the heights.

Would this cause the rear not to rise when going to normal height?

Would appreciate any thoughts before I dive into the wrong thing!

David.

[GiveMeABreak]

You should be able to get some live data on the suspension David. IT should show you the front and rear current values against the reference values - what are these showing?

[DHallworth]

Thanks Marc, I totally forgot you’d be able to interrogate each sensor with Diagbox.

I’ve had it plugged in tonight and have concluded that something is a miss with the rear right height sensor. It’s supposed to have had a new one so am wondering if it’s not seated properly, failing that, it looks like it’s knackered. The fronts aren’t right either I don’t think so I’ll get under it and have a proper look at the height sensors and the linkages.

Video below:



Hoping it’ll behave itself long enough to get an MOT on it tomorrow.

David.

[DHallworth]

Well, it's time for a long overdue update on this.

I (finally) bought a new (used) height sensor on eBay, fitted it and am getting exactly the same fault with exactly the same symptoms.

With the car on its lowest setting it won't come up to normal height, going to intermediate and then back down to normal does work though. When driving you can feel the rear of the car lower itself slightly, slowing down, raising the car to intermediate and putting it back down does restore the height again.

When parking the car and lowering the suspension, the front goes into it's lowest position, the rear of the car goes to the point where it looks like the car has been depressurised and the top of the wheels disappear into the wheel arches.

I was hoping that a new height sensor would have cured it but evidently not

David.

[GiveMeABreak]

Hi David

Assuming of course that nobody has changed the suspension height programming parameters and that these are reading within the reference heights, and that the height sensor clamp hasn't been moved (probably not if the height is returning to normal from intermediate), then I can only point a finger at the rear hydraulic block. The car bottoming out or dropping when driving are other symptoms of this. The valve can become stuck causing intermittent behaviour issues.

It's also documented on C6 owners IIRC

Have a look at the posts from 'cruiserphil' and his pics here:

http://c6owners.org/plugins/forum/forum ... hp?2638.30

I suspect the symptoms will be better or worse depending on the condition of the valve.

[DHallworth]

Thanks Marc,

What's confusing me is the fact it won't raise when dropped and the height sensors are giving odd readings. Got me puzzled on that one. There is a fault stored for reference heights not programmed though which is odd.

Another interesting point is that if I park it, it'll maintain the normal ride height for weeks so I'm not sure if it's the rear valve block or just a bad reading from the sensor that's confusing it.

David.

[GiveMeABreak]

Ok, so maybe it will help if I put the diagnostic info regarding the parameters up regarding the heights. This is for the Saloon - If it's for the Tourer let me know.

LEXIA/PROXIA title (*)	Unit	Value	Parameter Statuses
Doors And Tailgate Status	-	0	Plip
Doors And Tailgate Status	-	1	doors
Doors And Tailgate Status	-	2	battery unit
Steering Wheel Angle	°	-	XXX
Hydractive Status	-	0	Soft
Hydractive Status	-	1	Closed
Reference Height (Before )	Step	-	XXX
Reference Height (Rear )	Step	-	XXX
Front Filtered Height	Step	-	XXX
Rear Filtered Height	Step	-	XXX
Programmed Front Reference Height	Step	-	XXX
Programmed Rear Reference Height	Step	-	XXX
Initial Front Reference Height	Step	-	XXX
Initial Rear Reference Height	Step	-	XXX
Brake Status	-	0	Inactive
Brake Status	-	1	Active
Vehicle Speed	km/h	-	XXX

Parameters	Unit	Definition of the Parameter
Doors and tailgate status	-	Type of access which supplies the suspension ECU (Remote control, door, boot)
Steering wheel angle	°	Steering wheel turning angle . Only to be taken into account when driving (Not used on the current height correction version)
Hydractive status	-	Status of the hydractive (Firm or soft) The height cannot be corrected when the hydractive is at the firm status
Reference height (Before)	Step	This is the front height which the vehicle must reach (For the normal and track positions only) For the high and low positions, control until the stops are compressed. The values mentioned for the high and low positions are the heights which must be exceeded, but these reference values are not binding. This height varies in relation to the position (High, Track, Normal or Low) selected by the driver. When the driver selects the Normal position, the reference height is equal to the programmed reference height
Reference height (Rear)	Step	This is the height (rear) which the vehicle must reach (For the normal and track positions only) For the high and low positions, control until the stops are compressed. The values mentioned for the high and low positions are the heights which must be exceeded, but these reference values are not binding. When the driver selects the Normal position, the reference height is equal to the programmed reference height

parameters	Unit	Definition of the parameter
Front filtered height	Step	Front instantaneous actual height of the vehicle (This height is filtered at 7hz, therefore no wheel bounce is felt)
Rear filtered height	Step	Rear instantaneous actual height of the vehicle (This height is filtered at 7hz, therefore no wheel bounce is felt)
Programmed front reference height	Step	Front height which is programmed in the ECU when the vehicle reference heights are set. This height serves as a reference for the calculation of the vehicle reference heights
Programmed rear reference height	Step	Rear height which is programmed in the ECU when the vehicle reference heights are set. This height serves as a reference for the calculation of the vehicle reference heights
Initial front reference height	Step	Front height "hard" stored in the ECU, this height does not change and cannot be modified. This height is always equal to 128 steps at the front. This height serves as a reference until the reference heights programming procedure is carried out
Initial rear reference height	Step	Rear height "hard" stored in the ECU, this height does not change and cannot be modified. This height is always equal to 120 steps at the rear. This height serves as a reference until the reference heights programming procedure is carried out
Brake status	-	Status of activation of the brake pedal (active if the brake pedal is pressed, inactive if the brake pedal is released). Below 30 km/h, height corrections are prohibited while the brake information is active
Vehicle speed	km/h	Vehicle speed

Reference Heights
The initial heights are heights (front / rear) which are "hard" stored in the ECU, these heights do not change and cannot be modified.
These heights are (for Saloons) equal to 128 steps at the front and 120 steps at the rear and serve as a reference until the reference heights programming procedure has been carried out.
The programmed heights (front/rear) are programmed in the ECU when the vehicle reference heights are set.
The values displayed are based on the reference heights setting carried out previously.
These heights serve as a reference for the calculation of the vehicle reference heights.

[DHallworth]

Sorry Marc, I didn’t see your reply and realised that I’d never updated this.

The fault was cured by swapping out the Suspension ECU on the car. I’m not sure if the fault was to do with the programming or it it was to do with the ECU itself.

David.

[GiveMeABreak]

Better late than never David

Glad you have it all sorted.