Suspension gone harsh since battery disconnect

[Mechcanico Lee]

Hello all, had the battery off doing some tests and since re connect the suspension feels harsh like 100 psi in the tyres , no fault codes , suspension lifts up fine and drops back down all good .
Ride hide looks same as usual , jacking / towing mode not engaged , everything seems ok .
Is there some kind of re learns /adaptations to carry out when battery has been off ....... have had it diss connected previously with no troubles though .
Hope it's not spiked the module or something daft

Thanks in advance
Lee

[Johnmed]

How curious. I've never heard of that before. Sorry, this is no help to you Lee.

[paulrstaylor]

Hi Lee,

Sorry to her your having issues, never had any similar problems and I had the batter off a time or two while I owned the car!?

Hope it works itself out!

Paul

[Delboy]

I have heard of this before might have been on ross tech forum but cant remember what fixed it, was something simple like disconnecting battery or unplugging module but cant remember or find it again.

its basically the shocks not got power to soften the dampening like the emergency default

[snapdragon]

I have had this when I first bought the car and read of a couple of others on here - it was always after a flat battery. It always seemed to go away as suddenly as it came, but I would try disconnecting the battery for a few seconds.

[Mechcanico Lee]

Spent hours on this yesterday with vcds ,on further investigation I did think the car sat a little low ,specs for se are 415mm front and 400mm rear ,centre hub to wheel arch ......well to be precise it's 416mm front and 398mm but a couple of mm is hear na there ,mine was sitting at 380mm font 375 rear .
Tried removing battery lead again and a bit of driving round ( will get back to this ! ) , in dynamic mode it was terrible ...... May aswell of been dragged around on a shovel !



Coding of level control the double 5 meaning 0 change from base



Where I was getting a bit lost the double 55 being base I would of thought that in the calibration the desired height would of been 416 f and 398 r but it was not , can't remember what but it was a lower setting , so thought need to get it up to standard ride height so the air bags are at there optimum for a comfort ride , so changed the code to 99 + 20mm , this change got it to nearly factory spec ride height .



So test drive at standard ride height ...... it's better for sure but still not as silky smooth as before , I digress .....I took laptop with me on test drive and in comfort mode damping was showing in data blocks as 1.8 amps ... max amps =soft damping , min amps 0.2 amps or some such hard damping setting

When stood still damping is at hard setting , as you get above 10 mph damping reverts to softest setting but watching it on test drive it going from on extreme to the other 0.2 amp ... 1.8 amp sort of cycling effect ..... mmmmm


I was looking through the data and spotted this .....






As soon as I saw this I new what was wrong .... strut velocity ..... Eureka !!!

500 SL Mercs with hydractive advance body control suspension have similar .... I've done quite a bit of work on these , they have something called strut measurement rod , it runs through the middle of the strut and measures how it is reacting on the road , if the body battery ever goes flat the damping defaults to a hard setting .
You have to drive them in sport mode ( the hardest damping ) for a good 10 miles or more and the suspension ecm learns how the strut is reacting and dials the damping in , once sport is learned the comfort mode is just a softer map of that .

Are you still here or lost interest and gone to watch the paint drying ........

Back to the a8 ........ so in dynamic mode I set off on test drive maybe after 10 miles of shaking the fillings out of my teeth it starts to get a bit more plush on the ride .... keep driving .... it's getting better by far , switch over to comfort now ...... the plush ride is back to normal ...... it's the ecm learning the strut velocity and dialling it in to the damping map .

Still unsure with the ride height thing , don't understand why the double 5 coding is not the spec ride height , it looks a bit high now so will try it back at that setting .
In reflection I reckon if I just drive the car around in dynamic after I had the battery off everything would of sorted it's self out on its own ..... that's adaptive drive cycle for ya

What I think has happened originally , I had a shunt across the battery doing testing on how much amps is drawn when auxillary hearing kicks in , I was sort of mucking about trying to get a good contact so the battery was kind of connected then not then connected then not , it must of just upset the modules somewhat and defaulted it to safe , because I have had the battery off before with no adverse effects .



A battery shunt is a device that allows you to go inbetween the heavy cable so you can 'tap off ' and measure amps draw without blowing your multimeter all the time ..... just for those who was wondering don't cha know


Hard work typing all that on an iPhone ....... frekkin predictive text .... a tell thee ..

[Lee S]

That's very interesting. Didn't know that the struts were that complex. Cool. Glad it's sorted though.

[tc4332]

Well done Haydock Lee.
Surprising what comes out of the woodwork of experience.
Really would like you to attend one of our meetings.

[snapdragon]

Thanks for the detail - makes sense. ECUs scrambled after trying to start the car with a flat battery and bouncing your shunt probably have the same effect.

[Norretal]

I never cease to be amazed by the skills ( fault finding and manual) and knowledge of the members of this forum. As someone who is limited in those areas it's a huge comfort that I can call on their experience should something go wrong with my car, rather than be resigned to being ripped off by a stealer or anyone else.

Keep up the great work guys