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Advice on diagnosing an on-going "Suspension Faulty"

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mixolydian   
Wed Jul 31 2019, 05:10pm
Joined: Jan 03 2018
Member No: #3382
Location: South
Folks,

I know aspects of this have been discussed elsewhere, but I'm hoping someone might be able to shed some light on my issue given some specific details.

I’m finally getting around to fixing my C6's “Suspension Faulty” error (or attempting to, at least). There’s something of a backstory to this, but the basic problem is that the ride becomes very firm shortly after setting off from a standstill. It appears to start in the soft ‘comfort’ mode, then it throws the error and resorts to what I assume is a ‘known safe’ state after a few seconds. The suspension then remains in this setting until coming to a standstill, at which point it appears to soften-up until then setting off again and the process repeats.

I have some ideas but would appreciate any advice given the following:
- The car is a 2007 2.7 Executive
- Before I owned the car, the previous owner had a rear wishbone changed. I don’t know if this is time-correlated with the emergence of this fault and unfortunately, I have no way to practically verify it. I’m wondering if the garage they used fitted the wrong wishbone (i.e. a C5 unit with a different height sensor mount point)
- Lexia has complained about comms with one of the sensors (need to re-scan to confirm)
- Lexia has complained about the steering angle sensor (may be the ‘standard’ false positive). I’m skeptical because the directional headlamps work correctly and can’t see how this would be the case if the sensor was faulty
- The manual height adjustment functions correctly at all heights
- The car has four matched (newly fitted) Michelin Primacy 4 tyres with even wear
- Both driveshafts have been changed (genuine parts)
- I’ve had a local specialist look at it, including and initial ‘tweak’ followed by replacing two height sensors and fully calibrating them (genuine parts)
- I’ve not tried recalibrating the height sensors myself, which I’m now seriously thinking about
- I’ve not tried to replace or recalibrate the steering angle sensor (I’m concerned about making things worse if this isn’t the problem and just adding something else that I then need to fix)

My thinking is that the suspension controller is polling / awaiting data from a sensor that it never receives - doing this ’n’ times before then giving up and failing to the hard setting. Whilst I can’t back this up, it seems logical that the car would have some sort of preservation mode in the event that it can’t get a read on the actual vehicle height, therefore reducing travel and resulting in this harsher setting. It also seems broadly consistent with the information I’ve read on how the electronic controls systems for the suspension actually operate.

This does bring me back to either the height sensors or steering angle sensor. I’m starting to wonder about the calibration of the height sensors as I know that sometimes you have to do this a few times before it takes - I’m not sure whether the mechanic who did the work would have done this (though he’s a great guy). Equally I’m suspicious that this could all be the result of a botched wishbone change. I’m just about to arrange swapping out the fronts, so wonder if it’s worth getting them all done with parts I know to be correct (just to be sure).

I’m going to re-scan with Lexia to get an up-to-date view. As ever I would really appreciate any thoughts or ideas you guys might have. This has been a consistent fault in the nearly two years I’ve had the car, so I’m really keen to try and make some semblance of progress!

Many thanks.

C6Dave   
Wed Jul 31 2019, 05:58pm

Joined: Oct 01 2009
Member No: #1
Location: Northumberland
- Lexia has complained about the steering angle sensor (may be the ‘standard’ false positive).

I would ignore that one and concentrate on the height sensors 1st.

Now rather than changing all the wishbones etc. a used suspension ECU costs £60 from eBay - Click Here - and is a 15 minute job to swap as it sits under the enging bay fusebox cover and it's a couple of connectors and 2 screws to swap it....

Changing that would rule it in/out as the source of the problem if the ride heights are OK

EDIT: another thought. I read a post on the cruise control that wouldn't work and was tracked down to a faulty rear left ABS sensor sending the wrong info. Once changed, problem solved.

Now is it possible that the car, once moving, thinks it's doing motorway speed so is firming up the suspension because it's getting incorrect speed info?
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 mixolydian (01 August 2019)
cruiserphil   
Thu Aug 01 2019, 07:54am

Joined: Jan 24 2010
Member No: #38
Location: Celbridge
Hello Mixolydian,

As per C6Dave, don't waste time on the steering angle sensor. However, I would check the status of you height sensor programming. I upset the height programming once trying to set the car height levels and got the symptoms you have. I even got a replacement sensor for the one highlighted as in error which made no difference. When I sorted the programming error everything was fine. Also check the linkage bracket alignment to the wishbone.

Best regards,

Phil C.

1 User said Thank You to cruiserphil for this Post :
 mixolydian (01 August 2019)
Dowen   
Thu Aug 01 2019, 07:54am
Joined: Mar 04 2019
Member No: #3847
Location: Halesowen
When starting my c6 it would go straight to max height at front! I got "no communication " on lexia! Indi said I needed new bsi!£1200 !
I removed all connections from sus ecu and flooded with contact cleaner, let it dry off,
To my amazement, suspension back to normal.
Occams razor!! It's worth a try
2 User said Thank You to Dowen for this Post :
 mixolydian (01 August 2019) , cruiserphil (04 August 2019)
mixolydian   
Thu Aug 01 2019, 09:21pm
Joined: Jan 03 2018
Member No: #3382
Location: South
Thanks for all your response, folks. Massively appreciated and I'm going to have a look over the weekend. I'll get into the sensor configs first, just to satisfy myself that I have some data to back up my problem determination.

I'd not thought of replacing the suspension ECU so thanks for that - I may get one in any event, as I like to keep a set of 'sensible' spares. Equally, the contact cleaner is a good shout.

Thanks again - really useful to have some experienced input. I'll let you know how I get on.
1 User said Thank You to mixolydian for this Post :
 cruiserphil (04 August 2019)
mixolydian   
Thu Aug 01 2019, 09:30pm
Joined: Jan 03 2018
Member No: #3382
Location: South
Sorry, just spotted C6Dave's edit.

That's an interesting shout - it's had a new ABS sensor as that went last year. causing a range of interesting faults...

The cruise control does work when the steering wheel switch is functioning. That's really intermittent and I've tried the rake / reach adjustment + rotating the wheel just to see if it's a broken contact. It does *seem* like the switch is at fault as when it's on the system works correctly (cruise and speed limiting). The switch looked like it had been 'flash-dashed to death' when I bought the car as the face of the rubber was peeling. I might remove the assembly and check the switch operation for continuity with a multimeter.

Many thanks.

1 User said Thank You to mixolydian for this Post :
 cruiserphil (04 August 2019)
Nikola   
Sat Aug 10 2019, 07:49am
Joined: Aug 03 2018
Member No: #3613
Location: Beograd
Bay new linkage and livers they’re extremely cheap and easy to fix replace and set car for referent heights.
If Refereent height are not good car wil send you sunspesion fault error message.
Note for reference heights setting you have to go slowly dropping car for 10mm every time. Then check again and again. The Garage’s doesn’t take that time because in c5 that don’t couse any problem.
cruiserphil wrote ...

Hello Mixolydian,

As per C6Dave, don't waste time on the steering angle sensor. However, I would check the status of you height sensor programming. I upset the height programming once trying to set the car height levels and got the symptoms you have. I even got a replacement sensor for the one highlighted as in error which made no difference. When I sorted the programming error everything was fine. Also check the linkage bracket alignment to the wishbone.

Best regards,

Phil C.



1 User said Thank You to Nikola for this Post :
 cruiserphil (12 August 2019)
mixolydian   
Fri Jan 10 2020, 05:39pm
Joined: Jan 03 2018
Member No: #3382
Location: South
Folks,
Apologies for the delay in replying to this - a combination of work and frankly other C6 problems render this much less of a priority. I'd like to keep this going until it's fixed, since this might prove useful to someone else in the future.

In any case, I'm now back to this problem having solved the more urgent bits and pieces. Since my last post I've swapped out the Adaptive Suspension Controller (thanks to C6Dave for the recommendation) and she has new front duck's feet / bushes. I've checked the vehicle speed sensors using a combination of Lexia and a program I wrote to stream the VSS data back over the OBD-II port. They've checked out, so I'm comfortable they're okay. However, using the same approach I set up a logger that traps the 'Suspension Faulty' message whilst I'm driving - the messages appear 30 seconds after setting off from a standstill (each time), which seems far too deterministic not to be something sensor / software related.

I'm now going to re-set the heights and test connectivity to all the sensors. I have been unable to do this since before now because the only level surface I have is my garage floor - which has recently been occupied by another broken car (not a C6)!

I've also found there's a piloted deflector fault, which could well be some broken wiring in the bootlid loom. I don't see why this would be related, but I'll investigate it all the same.

I'll post back here with updates when I have them.

Many thanks.
C6Dave   
Fri Jan 10 2020, 06:39pm

Joined: Oct 01 2009
Member No: #1
Location: Northumberland
mixolydian wrote ...

I've also found there's a piloted deflector fault, which could well be some broken wiring in the bootlid loom. I don't see why this would be related, but I'll investigate it all the same.

There are a lot of interconnected items via the CAN system with some often surprising outcomes so don't rule anything out.

The spoiler activation is 'speed' related as is suspension control.
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rwb   
Sat Jan 11 2020, 01:00pm
Joined: Dec 22 2014
Member No: #1988
Location: Telford
Exactly what I had after my driveshafts were changed.

Here's my thread: - Click Here -

TL;DR: subtract the sensor values from the ideal values before entering them into the height programming. I don't understand why this worked. I expect that consequently my car is at the wrong height.
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mixolydian   
Sat Jan 11 2020, 05:24pm
Joined: Jan 03 2018
Member No: #3382
Location: South
Update - I've been running some diagnostics and have a few results to share. The good news is that all four height sensors have good voltage and provide continuous output. Whilst capturing the travel values for each corner I also collected the variable damping data, meaning they're on the same time axis.

The "Suspension Faulty" error correlates precisely with the variable damping value 'flat lining' at ~013. When pulling to a halt, the system then kicks-in once more and the values change until the next error is thrown after about 30 seconds of continuous driving.

The negative values for the front right and rear left suspension, I think, tell me that the calibration is just plain wrong. This is interesting because it has been set-up by a specialist a few times. However, the last time was definitely off as the front-end was far too high.

My hypothesis (guess) is that the variable damping ECU is seeing this negative movement as 'bad data' and giving up after a pre-defined wait period - which is ~30 seconds, based on my experience.

Here's my current thinking - recalibrate the sensors / reference heights based on new, flat-ground measurements. Save the calibration and re-run the test with live capture running for these same data points.

Any thoughts gratefully received.









2 User said Thank You to mixolydian for this Post :
 cruiserphil (11 January 2020) , Tjensen (12 January 2020)
rwb   
Sat Jan 11 2020, 09:00pm
Joined: Dec 22 2014
Member No: #1988
Location: Telford
If you take the same physical sensor and rotate it from one side in order to fit it onto the other side then doesn't that mean that its value reads in the opposite sense?

I saw the value on one side being approximately the negative of the value on the other side.

Interesting find that after the fault the damping goes to a constant value.

But, indeed, I can't see anything wrong there.

So I think we have the same problem that this is something to do with programming the heights.

So:
* theoretical radius of 245/45R18 is 335
* front K1M standard value is 160 which means that you should measure H1M to be 175.
* rear K1M standard is 111 which means that you should measure H1M to be 224.

The tech doc describes a tolerance of 6, but doesn't say what to do if you're outside of this.
But I don't understand this because if the measured height is outside of the desired range then surely Diagbox should accept the values and the suspension should adjust itself?

Using 160 and 111 was failing, so I subtracted the sensor value from K1M and those values were accepted.

(I didn't actually measure because it was cold and wet.)

I have no idea why this worked, and I haven't been able to formulate any plausible hypotheses.
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 cruiserphil (11 January 2020)
cruiserphil   
Sat Jan 11 2020, 10:01pm

Joined: Jan 24 2010
Member No: #38
Location: Celbridge
Hello rwb,

I'm completing fitting wishbone bushes tomorrow and will be checking/programming vehicle heights with Diagbox. I will let you know how I get on and if I had the complications I had years ago Lexia.

Best regards,

Phil C.
1 User said Thank You to cruiserphil for this Post :
 321dave (12 January 2020)
mixolydian   
Sun Jan 12 2020, 11:18am
Joined: Jan 03 2018
Member No: #3382
Location: South
Another short update: no material progress, I'm afraid. I've tried various approaches but consistently get the "Programming failed..." error, after entering the Rx and HxM values.

What strikes me as odd is that though I always get this error, it does appear to have an effect. The height does adjust after it's thrown the error and I can see changes when reviewing the Standard Parameter telemetry in Diagbox.

The negative values show the reference is wrong, but she's really not playing ball with these errors. I'll persevere and provide an update later on.

Thanks again for everyone's input, much appreciated.

2 User said Thank You to mixolydian for this Post :
 321dave (12 January 2020) , cruiserphil (13 January 2020)
cruiserphil   
Mon Jan 13 2020, 10:04am

Joined: Jan 24 2010
Member No: #38
Location: Celbridge
Hello Mixolydian,

Have you tried the method of inputting the virtual HxM values to get you to where you want to go. I know when I input values as measured the car went from OK to programming failed.

I didn't get to height correction this weekend as planned but hopefully during the week and let you know what happens.

Best regards,

Phil C.
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