C5 mk1 rear going up/down when parked

[teuski]

I adjusted the rear height of my new mk1 C5 since it was too high. Now after that when parked the rear end sinks a few centimeters, then raises up and the cycle repeats about once per 10 seconds. It happens when the car is running and when the ignition is off and continues for at least 15 minutes, probably until economy mode kicks in.

I wonder if the height sensor got somehow messed up?

[GiveMeABreak]

Very likely. The rear suspension is now likely out of the allowed reference height parameters, so the BHI is now constantly compensating. This will be a sure way to prematurely wear out the electronic pump and flatten the battery.

If you suspected the rear height corrector, I would of cleaned it up and lubricated it before moving or adjusting it. Always carefully mark the current position before adjusting. If you cannot return it to the original position, you may have to programme the height references in using the formula and procedure with Lexia.

[Paul-R]

How did you adjust the height? Did you physically move the sensor on the anti-roll bar or did you alter the parameters using a Lexia/Diagbox? Or was it a combination of the two?

[teuski]

I did it just by moving the sensor on the anti-roll bar. That has always been enough but seems like i'll have to check it out with Lexia.

Could someone tell the correct procedure for setting the reference height? I remember trying to do it a few times but couldn't manage to make it work.

[Mandrake]

Are the rear suspension arm bearings worn out and stiff to move ?

"Hunting" where the height correction keeps overshooting upwards and downwards can happen if the suspension can't move freely and easily.

Try pushing the suspension by hand - it should move freely, if you have to push hard before it moves at all and then it suddenly "lets go" you might have worn out arm bearings.

[GiveMeABreak]

It's odd that this would only start happening after he adjusted the heights in the first place though Simon. I would of expected that to be happening prior to the adjustment he made - but he said it was just a bit high.

@Teuski: I've emailed you the PDF procedure for checking and correcting the heights in case Simon's suggestion isn't the issue.

[Paul-R]

I had to replace the rear height control potentiometer (the "sensor") on my old Mk1 C5 when the dog-leg rusted off. I tried very hard to adjust the height correctly with my Lexia but the readings didn't seem to make sense and in the end I did it by rotating the potentiometer on the A/R bar.

I had to return the car to the road (I had been using axle stands of course) and then cycle through some high/low adjustments to get the car on to its median position before I found the correct height. It didn't take very long - less than half an hour.

When you put the replacement pot on the A/R bar did you get it the right way round with the dog-leg connector? Was the dog-leg moving freely in the ball joints?

[teuski]

Thanks all for your comments! And GiveMeABreak for the guide pdf, i will try to set the new reference height with that.

The rear arm bearings are not in a bad shape (i have experience of some really bad ones). The sensor is in correct position. I only removed the bracket from the anti-roll bar and welded a nut to it for the tightening screw since the original thread went bad.

The rear end was quite high and i lowered it for maybe 5cm so it sounds reasonable that i might have gone out of the reference height range. If the sensor is worn it definitely got some excercise yesterday The dogleg is moving well.

[GiveMeABreak]

No problems, let us know how you get on when you've completed the procedure.

[Paul-R]

Disregarding the cycling is the rear now at the correct height? For instance, when driving at night are the headlamp dip beams correctly adjusted?

A couple more things you could try first. Give the car a couple of rounds of citroearobics and then check the level of the LDS fluid. You could check the level before the citroearobics as well.

[Mandrake]

It's odd that this would only start happening after he adjusted the heights in the first place though Simon. I would of expected that to be happening prior to the adjustment he made - but he said it was just a bit high.

I agree it's odd, but cycling up and down is usually due to stiffness in movement causing an overshoot. I wonder if it is actually the height sensor movement that is not smooth and is seizing ? That would have much the same effect...

With the end of the car safely up on RAMPS, I would be inclined to disconnect the sensor from the roll bar and manually operate the sensor arm to see it the height oscillates then too, or whether there is the expected height change of the car for a given sensor arm movement.

It should be possible to find a sensor arm position where the height remains constant, and it should move up or down smoothly if you go either side of that.

[teuski]

Ok, problem solved.

My measured heights were almost the correct ones, but i couldn't get lexia to accept my values (front: 280-H1M+R1 = 280-310mm+175mm=145 / rear: H2M-R2 = 380mm-310mm=70).

When i checked suspension parameters i noticed the "rear filtered height" changing from 12 to "normal" 128 steps when the rear rose up and then dropped to 12 again.
Then i realised the sensor must be 180 degrees the wrong way abd turning it the other way solved the problem.

One could easily think it's a limited travel potentiometer, but seems like it rotates around and has 256 positions.

Now that i think of it remember seeing a pic of an opened sensor and that the position is detected optically...

[Paul-R]

Then i realised the sensor must be 180 degrees the wrong way abd turning it the other way solved the problem.

Hence my question-

When you put the replacement pot on the A/R bar did you get it the right way round with the dog-leg connector?

In my case I had the old one and the replacement one next to each other when replacing old with new but when there is a time lapse I find it helpful to take copious photographs.

[teuski]

I didn't take the sensor off, just the bracket on the other end. I left the connecting rod to the sensor but somehow put it back the wrong way.

[GiveMeABreak]

Glad it's all sorted