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Advice on diagnosing an on-going "Suspension Faulty"
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mixolydian   
Tue Jan 14 2020, 06:06pm
Joined: Jan 03 2018
Member No: #3382
Location: South
 Folks,

Success!

I'm pleased to say that I now have the suspension working correctly. The error is no longer being thrown and the variable damping / travel sensors appear to be functioning as intended. The breakthrough was on Sunday, but I confess to holding off on this update until I'd put some mileage on the car. ~250 miles later, she's in good shape.

The 'programming failed' message proved somewhat erroneous. Even though I received this after setting the reference heights, I would see / feel the car moving when the new values had been set. As per @cruiserphil mentioned (many thanks for this), the car accepts relative values providing they're in a range it can take.

To be honest, I'm still going through the data as I worked through quite a lot different combinations for the values at each corner (~50). I took and re-took the actual measurements, but ended-up settling for something more idealised. The set-up appears to be based on optimising three attributes:

1.) The actual values input for the R and HxM variables;
2.) The per-axle variation from left-to-right; and
3.) The front-to-back variation.

As has been mentioned, the CSS ECU calculates the 'right' value based on the values you give as input.

Obviously we don't really know what this function is, or indeed that it's purely a function of the data we put in. I used so many combinations as I wanted to try to model what impact these variations have on the values the ECU finally applies - as visible in the 'learnings' data in the Standard Parameter sub-menus.

It's hardly rigorous regression analysis, but I started to get a sense of how manipulating the FL, FR, RL, RR settings influenced the final calibration. The ECU will throw other errors if it the front axle left-right delta is too high, similarly so with the front-rear. I suspect, but don't know, this is in proportion to the total amount of correction the system can apply through the stepper motors - viz. if the total variance exceeds the tolerance, then the system will fail to a 'safe' setting.

In my idealised values I worked with the actual values as a mid point, correcting either side of this according to the positive / negative values I'd seen on the travel sensors. Effectively, treating it as a weighted mean. The important part is to review the 'learnings' data from the parameter measurement sub-menu and not making large changes in one go. I think this has been mentioned elsewhere on the forum, but the system possibly guards against large changes to protect it from errors / typos when programming. I found this to be the case when testing the hypothesis with my car.

I may still make a few other changes, but I'm enormously pleased to have everything working. The ride really is sublime. Once I have things finalised, I'll look at sharing the settings / trace data as before.

Thanks again to everyone who helped out - it's massively appreciated.

Mixolydian.
cruiserphil   
Wed Jan 15 2020, 09:56am

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

Well done. Thanks for posting your success and analysis.

Best regards,

Phil C.
kitch   
Tue Dec 08 2020, 10:04am
Joined: Sep 19 2020
Member No: #4485
Location: Hampshire
 Hi guys, many thanks for this thread. I've been reading in detail as I have exactly the same symptoms (though I need to check whether my fault occurs after the 30secs point, as I think mine may vary more than that).

I'm planning to reset the suspension heights myself (like you, OP, mine were done by a specialist prior to my purchasing of the car). I've bought new brackets, have a couple of used sensors, and even bought the PSA hub tool to attach to the wheel bolts and measure from!


Only issue is my DiagBox is jammed in French (and refuses to do anything else!) So work on the laptop is slow at the best of times.
kitch   
Tue Dec 08 2020, 01:59pm
Joined: Sep 19 2020
Member No: #4485
Location: Hampshire
 To follow up my last post, I went for a drive at lunch, and lo & behold, it's 30secs.

The reason for my questioning is that it seems it's 30secs from the point the suspension starts 'working'. If you drive down a dead smooth road, and barely cause the suspension to compress/extend, it'll remain fault-free, but as soon as the suspension reaches a certain threshold for travel/demand, the 30sec countdown begins. And it's repeatable, too.

Drop below 10mph, and the fault disappears and the process begins again. I'm so grateful you posted this, because it gives me an avenue to try!
kitch   
Thu Dec 10 2020, 09:57am
Joined: Sep 19 2020
Member No: #4485
Location: Hampshire
 Second follow up!

That evening, I hooked up Diagbox and attempted to read and correct the axle heights. Time was pressing, so I guessed the front as an experiment to see what (if anything changed).
On entering the numbers, the front lowered immediately, but the rear stayed the same. It then told me it had failed to calculate the measurements, and to try again.
I didn't try again because I didn't have time, so drove home as-was...without the fault! The front is now too low, because it's bottoming out (though it is cornering very nicely!) At a risk of oversimplifying things, I'm wondering if the front height sensors are worn (150k mile car) and because the front end is now sitting at a slightly different height, whether the sensors are getting a chance to read better.
I have some used sensors (lower mileage) so will try fitting those, along with some brand new linkages and brackets I've got. Then I'll measure it all precisely and enter those numbers in, and see where we end up.

Thanks again.
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