C5 Rear Suspension Issues

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vealg
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C5 Rear Suspension Issues

Post by vealg »

Hi,
I have a 59 plate C5 3.0 HDI Exclusive Saloon and the rear suspension has started to collapse when the car is switched off. There is a hissing sound coming from the unit underneath that all the hydraulic pipes feed into and after trying to raise the suspension the rear suddenly shot up and seems to keep adjusting itself.

Can anyone provide any advice and is the car safe to drive?

Thanks

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GiveMeABreak
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Re: C5 Rear Suspension Issues

Post by GiveMeABreak »

Hi

This smacks of your height corrector(s). Post up your VIN (or PM it) and I'll check variant as I suspect on the 3.0 litre, you'll have height correctors on all 4 wheels.

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myglaren
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Re: C5 Rear Suspension Issues

Post by myglaren »

Electrovalve leaking?

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GiveMeABreak
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Re: C5 Rear Suspension Issues

Post by GiveMeABreak »

Yes, possible Steve, could also be the rear hydraulic block housing the rear firmness regulator. Ideally he would need to get it on Diagbox to see what it's reporting (if anything) as you'll get no indication if any of the actual spheres are ruptured, but the actuator tests can be run to test the firmness regulator switching between Normal and Sport Mode and of course testing the ride heights. I think this has to be the next step really.

On a 4 cylinder, it uses the standard Front and Rear height correctors on the axles, but on the V6 models it has a corrector on each wheel instead - so if one of the rear wheel correctors is out of kilter, the variable suspension ECU may be adjusting the rear suspension to account for the faulty reading from one corrector - but then if the other rear corrector is working properly, the suspension ECU may be rapidly compensating again.

One thing is certain - if the car is trying to keep compensating for the ride heigh anomalies, this will put undue strain on the hydraulic pump motor and on the battery to keep operating it. The system remains operative for some time after the car is locked. So I would certainly get it checked out sooner rather than later.

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myglaren
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Re: C5 Rear Suspension Issues

Post by myglaren »

As it is when the engine is off I would presume the height correctors would be dormant and the problem a mechanical one, as in a stuck open electrovalve.

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EDC5
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Re: C5 Rear Suspension Issues

Post by EDC5 »

So the V6 models have a height corrector per wheel, but the height can only be modified per axle? Does the suspension ECU just average the values of the two height sensors per axle?

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Re: C5 Rear Suspension Issues

Post by GiveMeABreak »

It works differently to calculate the settings of the 4 sensor model over the 2 sensor versions, I’ll get a diagram when I get a minute.

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Re: C5 Rear Suspension Issues

Post by GiveMeABreak »

myglaren wrote:
29 Aug 2018, 20:50
As it is when the engine is off I would presume the height correctors would be dormant and the problem a mechanical one, as in a stuck open electrovalve.
Actually Steve the system operates without the engine running. I can quite happily load my car up with the keys in my pocket and the suspension will keep the car level as I fill up the boot. It generally switches off after a time when the car is locked and the electrovalves keep the car from sinking.

When unlocking the car next morning it will adjust slightly to get back to proper level , but the system can run without engine on. So if the corrector (s) are out of kilter, it can cause the system to play up during this operational period.

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myglaren
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Re: C5 Rear Suspension Issues

Post by myglaren »

Mine is similar but will only sink very slightly overnight, lifts a few millimetres on unlocking.

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Re: C5 Rear Suspension Issues

Post by vealg »

Just a bit of an update, forgive me I'm not very technical!

When I switch off the car, the rear suspension intermittently starts to drop and there is a hissing from the rear hydraulic block and the pump stays on but the car continues to sink. Eventually the rear collapses completely and when I restart the car the rear does not rise until after a minute or so at which point there is a load bang and the rear shoots upwards and then seems to level out. It seems fine when driving it after that.
It does not happen all the time and was fine overnight and seems to be OK so far today.
My concern is if this is going to be a very expensive fix then it may not be worth doing and will have to scrap the car which would be a real shame as it's fantastic overall.

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Re: C5 Rear Suspension Issues

Post by GiveMeABreak »

As per my last post - can you PM or post your VIN so we can see exactly which setup you have.

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Re: C5 Rear Suspension Issues

Post by vealg »

VIN number is VF7**************[VIN obfuscated, can be read by forum staff]*********
Last edited by GiveMeABreak on 30 Aug 2018, 21:10, edited 1 time in total.
Reason: VIN Masked

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Re: C5 Rear Suspension Issues

Post by GiveMeABreak »

Ok, so confirmed as 3.0 Hdi 6 Cylinder variant, so you have the height corrector sensor on each wheel as per the diagram below:
X7 6 Cyl Front Height Correctors.PNG
X7 6 Cyl Rear Height Correctors.PNG
C5 X7 Front Height Correctors on Each WheelC5 X7 Rear Height Correctors on Each Wheel
The anti-sinking function is carried out by the exhaust solenoid valves, incorporated in the integrated hydroelectronic unit (BHI) as shown below, so if the car is sinking at the rear, this may indicate the valve is playing up - I would check all the electrical connections to the BHI, to make sure they are secure and that there are no fluid leaks (now or previously, that may have caused fluid to get into the connectors.
X7 C5 BHI.PNG
BHI Integrated Hydroelectric Block (BHI) Showing Connectors

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Re: C5 Rear Suspension Issues

Post by Sloppysod »

EDC5 wrote:
29 Aug 2018, 21:16
So the V6 models have a height corrector per wheel, but the height can only be modified per axle? Does the suspension ECU just average the values of the two height sensors per axle?

Does this mean the V6 models have a better ride, similar to the C6?

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Re: C5 Rear Suspension Issues

Post by GiveMeABreak »

No Stu - none of the X7s have the AMVAR function that was available on some of the top end C6s. On the X7 V6 models the system incorporates a separate Suspension ECU and 4 height sensors (1 on each wheel) for these engines. Makes no difference to the ride. It's just there are 4 of the blighters to go wrong instead of 2!