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Wonky suspension

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Mon Dec 16 2019, 01:37pm
Joined: Dec 19 2010
Member No: #320
Location: Bedfordshire
Think it would best to get your car checked by someone completely familiar with C6.
You could keep changing parts for ever and not fix your fault.
If the front lower suspension arm from a C5 is fitted to a C6 you can get suspension faulty warnings.
The parts look the same but have fractionally different dimensions, enough to confuse the computer.
Mon Dec 16 2019, 02:00pm
Joined: Sep 28 2012
Member No: #1043
Location: south west
This was a most helpful procedure from "Cruiserphil" when I had a similar fault after work on N/S and O/S suspension.
years ago.
Sun Jan 15 2012, 07:37pm

I finally sorted out the failed programming of front right hand height sensor but it took about a day plus a lot of head scratching and trial and error. However, what I found I think will be of interest to those of you who try this out as just following the step by step instructions in Lexia may not be enough. You may need to do some corrective maths.

First follow the measurement instructions in the maintenance instruction (available in C6 owners). Effectively, you measure each actual wheel radius (including tyre) Rx and the height of the respective vehicle measuring points, HxM on the front and rear subframes. The target is to get the each wheel height KxM = Rx-HxM to be 160+/-6mm for the front and 111+/-6mm for the rear. So for example my front LH wheel radius R1 is 310 mm, so to get K1M = 160 mm I needed to measure H1M = 150mm. The rear RH wheel radius R4 is 320mm, so to get K4M = 111mm I needed to measure H4M = 209 mm.

When I changed the wishbones, the maintenance instruction advised to reprogramme the vehicle heights. So I hooked up Lexia. To set vehicle height you go -> DIAGNOSIS -> GLOBAL TEST -> VARIABLE DAMPING -> SPECIFIC AFTER SALES OPERATIONS.

Basically the procedure is that it asks you to enter each of your Rx and associated Hx measurements as you find them. This I did and the actual measurements were: R1 (front LH) = 310mm / H1M =124mm, R2 (Front RH) = 310mm / H2M = 126mm, R3 (rear LH) = 318mm / H3M = 207mm and R4 (rear RH) =320mm and H4M = 210mm. So , the rear was in spec. but the front was nominally 25mm too low.

So I thought that, once programmed, the car would know where actually it was and then with its sensors make the calculation and correct the car height. No!

It continually threw up "programming failed" and said check sensors, wiring etc. By going VARIABLE DAMPING -> PARAMETER MEASUREMENTS -> STANDARD PARAMETERS - > PROGRAMMING STATUSES it displayed that front RH sensor programming was INCORRECT. Countless repeat inputs failed. I decided to replace the RH sensor. In the interim the car's front suspension became stiffer - I think this is a default mode in the case of an incorrectly programmed or defective sensor.

I replaced the RH sensor but effectively no change. The breakthrough was going VARIABLE DAMPING -> PARAMETER MEASUREMENTS - > STANDARD PARAMETER MEASUREMENTS -> HEIGHT CORRECTIONS.

However, for front right hand movement, the figure was showing about - 20mm. This means that the system was saying that the front right hand was 20mm higher than the reference height. But if anything, it was 20mm lower. I decided to correct for this by adding 20mm to my H2M reading making it 146mm. Repeated the programming and voila - "programming done."

I took the car for a spin and the suspension was lovely again. However, the front was still 20mm lower. So cheekily I decided to tell the car that it was 20mm lower than it actually was. So H1M became 104mm and H2M became 106mm. Programme again - programming done and voila - cars raises 20mm.

So I fine tuned again and this brings me to what I find is what you need to do:

Measure your wheel radii R1 - R4.

Measure your heights H1M - H4M.

Work out the K1M - K4M. If a KxM is greater than the spec. subtract the difference from your HxM. If a KxM is less than the spec. add the difference to your HxM.

Check the movement for each sensor. If the value is positive it is saying that that the height is below the reference height by that amount. So subtract that height also from the relevant HxM. If the value is negative it is saying that the height is above the reference height by that amount. So add that height also to the relevant HxM.

Programme again.

It will ask you to reenter the figures after getting you to force height correction at each end of the car by pressing down in turn. For these figures, enter the actual values for HxM you measure again at this point.

So at the finish I ended up with K1M = 160mm, K2M = 162mm, K3M = 106mm and K4M = 106mm.

Took the car for a spin and suspension lovely.

Notice too that in the screenshot all the widely -ve and +ve height corrections have disappeared.

I hope this is of help and I needed to write it down before I forgot what I had done. At one point I feared I had a faulty suspension ECU.

Finally, anyone in need of a second hand RH front height sensor?


Phil C.
3 User said Thank You to speedfix for this Post :
 rwb (16 December 2019) , cruiserphil (17 December 2019) , Fraunie (17 December 2019)
Mon Dec 16 2019, 09:26pm
Joined: Dec 22 2014
Member No: #1988
Location: Telford
Thank you; this is something concrete I can try and sounds promising...

Symptoms are familiar: hard suspension. Absolutely horrible going over all the expansion joints in the M6 viaducts today.

Wrong wishbones is a red herring here because it was all working before I had new driveshafts.

I did notice a big difference between the front left and right values in parameter measuments. I thought that should be relevant somehow.

So it sounds like I need to be looking at height correction parameters and working back from there to obtain height programming values.

(Theoretical wheel radius for 245/45R18 is 339mm.)

I'll have a go tomorrow...
Tue Dec 17 2019, 12:41pm
Joined: Sep 28 2012
Member No: #1043
Location: south west
Just to add the suspension on the C6 when working ok has passed the test being superior compared to my Tesla MS with smart air suspension, not just me but from passengers being in the motor trade.

The other interesting point is that the ease of access in better on the C6.

Must do the door check stops though!

Wed Dec 18 2019, 04:25pm
Joined: Dec 22 2014
Member No: #1988
Location: Telford

Theoretical value of Rx for 245/45R18 is 339.

Measured height HxM
Calculate KxM = Rx - HxM which thus is smaller if the car is higher up.

Expected for KxM are 0160 front, and 0111 rear (so front is lower).

That means that HxM should be about 179 (front) and 228 (rear).

Sensor values
FL: -023.03 FR: 026.96
RL: 013.46 RR: -005.53

Programming values
FL: 174.92 FR: 174.92
RL: 223.91 RR: 223.91

It would appear that to obtain the "programming values" the computer has undone the KxM calculation.

FL is showing as correct, and the other three as incorrect.

I have checked that the links on the sensors are on the inside as Diagbox suggests (the sensors move all the way round).
Wed Dec 18 2019, 05:49pm
Joined: May 21 2017
Member No: #3151
Location: South Queensferry
rwb wrote ...


Theoretical value of Rx for 245/45R18 is 339.

Yes but that's with no load on the wheels. Measured Rx from the ground will be less. Mine are approx 310 front & 325 rear.

1 User said Thank You to MGmike for this Post :
 cruiserphil (19 December 2019)
Thu Dec 19 2019, 09:33am
Joined: Dec 22 2014
Member No: #1988
Location: Telford
Just completed my first 150 miles with working suspension and driveshafts!

I didn't actually measure the heights because I haven't found the front measuring points and because I didn't fancy finding somewhere flat to roll around on the floor in the cold and wet looking for them, so I just used the expected values of 160 and 111.

Then I subtracted the sensor values.

Diagbox said programming failed, but the error has gone!
Thu Dec 19 2019, 10:59am
Joined: Sep 28 2012
Member No: #1043
Location: south west
Carried out the height measurements on a platform lift however after setting up after several attempts I to had programming failed.

I found after a run and a slight correction on one wheel in Lexia the programming
came up ok.

I think from memory it was due to one in-correct tyre pressure.

I had to carry out the job due to new front shock replacement years ago when I bought car.

Well done doing the job, if all else is ok then the ride IMO is second to none.

Thu Dec 19 2019, 04:06pm
Joined: Dec 22 2014
Member No: #1988
Location: Telford
So I think the question is: what are the reasons that Diagbox will fail to programme the suspension?

Gut feeling is that it's something to do with the sensor values being too far away from zero -- possibly because of bent brackets. I did notice that the sensors go round and round and round, and indeed Diagbox says to check "the linkages are towards the inside" (which I did, and they were).
1 User said Thank You to rwb for this Post :
 cruiserphil (20 December 2019)
Thu Dec 19 2019, 06:37pm
Joined: Sep 28 2012
Member No: #1043
Location: south west
Gosh this brings back memories, this may help, first, when the service suspension warning came on after the shocks were fitted, I found the ball end links on my car had lots of wear in them so thought I would do a temp job so squeezed taking the wear out of the worn balls in place with a pair of mole-grips.

Using PTFE spray grease to complete the job and I still have not round to fitting new ones.

Still had the warning but not so much but the ride was far from what it should be,this then was the start of setting the of the suspension with the use of Lexia.

I am sure you are correct in that a bent bracket is the cause but even with new fitted I think the suspension ECU has already gone out of sink.

Could not have done it without Cruiserphil posting.

1 User said Thank You to speedfix for this Post :
 cruiserphil (20 December 2019)
Fri Jan 10 2020, 05:49pm
Joined: Jan 03 2018
Member No: #3382
Location: South
Hello rwb,

I fear we might be in the same boat - a particularly crashy given the hardened suspension. I have pretty much the same issue
- Click Here - and despite a combination of investigations from a local independent specialist and myself, it's proving a stubborn fix. It's interesting that you've had some variability in the error being generated - mine is consistent at 30 seconds after setting off, after which it becomes very stiff and then returns to 'comfort' when pulling-up to a standstill. This has been consistent despite changing the sensors.

We've done quite a lot of the same fault finding and I'm about to have another go at mine over the next week. I'll let you know if I find anything useful.

Many thanks.
Sat Jan 11 2020, 12:58pm
Joined: Dec 22 2014
Member No: #1988
Location: Telford
It sounds like it. I just came here to get the link to this thread to post on your thread!

The trick for me was to subtract the sensor values from the default values -- which I know is a hack. It's been fine since, but I expect that the actual height of the car off the ground is wrong.

(Also, my two front sensor brackets were both bent, in different directions.)

From what I've read in your case I'd want to check that you get ride height values in live data for all 4 sensors and that you can see these values changing when you change the height and when you drive around, and therefore deduce that you have four working sensors.

In my case it was noticeable that with the car on level ground the four sensor values were quite different. I don't know if this is significant or not.

On the one hand "no" because the sensors move by such a tiny distance that I don't see how it would be feasible to get them all to match at the same value.

On the other hand "yes" because subtracting the sensor values from the ideal values shut it up.
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