Height suspension / sensor issue - can't calibrate

Hi guys - need some help diagnosing my issues with my L320 2011 TDv6.

I was having some issues with air suspension faults coming on over last couple of months. I would get intermittent orange suspension fault. If I go over 65km/h for over 20secs then it goes into red suspension fault mode and goes down to bump stops.

I was having intermittent issues with the rear right height sensor so I changed this (using live values and Thingdiag tool). I also changed the front right height sensor after seeing some intermittent issues on this sensor also. I have also cleaned both front and rear valve blocks - were slightly dirty but were both fine.

Symptoms -
- as above I am getting intermittent orange suspension faults
- going over 65km/h for over 20secs I get a red suspension fault and it will go down to bump stops
- if i try put the car into access height mode it will go down and then go into extended height mode almost immediately
- trying to use thinkdiag tool to do a height calibratation - i can't complete this successfully (measuring heights from middle of hubcap to wheel arch). I suspect the measurements are outside acceptable values but not sure (436mm, 435mm on front left and front right, 483 and 473 on rears).

I have taken a live screen recording of the voltages I am seeing for each height sensor. You can see below -

- Graph 0-10secs - Initially the car is at normal height at the start. Readings are flat
- Graph 10-15secs - I then put the car into access mode. Front left and Rear left voltages go up while rear right and front right voltages go down. THIS I suspect is the issue. The voltages on one of the sides is going the wrong way when the car changes heights.
- Graph 15-20secs - After a few secs the go car goes into extended height mode and you can see the voltages go the other way to what they did initially when the car when into access height mode.
- Graph 25-50secs - Then period of flat area - car is in normal height mode.
- Graph 50-70secs - Car is put into off road height mode.
- Graph 70-90secs - Car is put into normal height mode.

As you can see the voltages on one side are going in the opposite direction to the other side. From this video - I think the issue are the sensors on the left side of the car - both front and rear left.

Can somebody sanity check the above? Is there anything else I should be doing to diagnose.

I swapped the sensors on the fronts to rule out any issues and it looks like this is how they are supposed to function - inverted on side to side. So after ruling out any more sensor issues I figured I just had to get through calibration somehow.

I tried a couple of times - I put in values that were close to what it was expecting (not the actual measurements) - and it got further where it lifts the car up to off-road height then brings back down and asks for you to measure again. I couldn't get through the second round because the calibration wasn't within 4mm error tolerance. I tried 3-4 times to get through but couldn't.

Even though I failed the full height calibration it seems to have taken values because now I am not getting any errors (orange or red) and everything seems to be working!!

They should not have those glitches ? I assume they are resistive sensors. Glitches indicate the sensor tracks are worn (or knackered)

The voltages look acceptable, there is 'smoothing' applied in the control module and the front & rear react differently. The traces seem broadly similar front L&R and rear L&R and the voltages seem within the range limits given the video resolution.



Calibration can be a fickle mistress on older vehicles, especially if you've had to 'apply some reverse torque' to remove a sensor. The brackets are easily distorted and 1-2mm at the bracket can be the difference between passing calibration plausibility - or not.
Sometimes you need to do one or two intermediate calibrations using calculated values to pass the checks to get it within tolerance for the 'real' measurements to be acceptable. I've also had to 'adjust' brackets - particularly L405 front sensors due to corrosion weakening the steel.