Hi all,

I live in Australia so I normally post on Aulro, but their site has been down for a while and we need our Land Rover back on the road so I'm hoping someone here can offer their expertise.

We have a 2000 Land Rover Discovery 2 TD5 Auto. We've been having issues with our air suspension (which we love and will never replace with springs). Initially the compressor died (one of the brush springs in the motor had corroded and snapped) because LR sensibly positioned one of the drain hoses exactly over the top of the SLS compressor's air intake filter in the left brake light assembly, but we put a new compressor on. Then it pumped up, but while driving it we noticed that if we braked suddenly and the car tipped forwards it would drop right down to its bumpstops until turned off and on again. We bought a Nanocom to help diagnose the issue (and because we've wanted one for years because... Land Rover...), and within about 5 minutes of plugging the NC in I saw the issue.

It turns out the voltage for the left side height sensor is varying wildy. Sometimes it stays consistent at 4.95V and starts to pump up but then it (the voltage) randomly starts dropping. Naturally the sensor value read by the ECU varies wildly as well. My first thought was that maybe the wires to the sensor were broken, but I pulled the plug out and inspected the wires as best as possible and could see no breaks. Unfortunately it kind of seems to me like it might be a failing voltage regulator in the SLABS ECU or something along those lines, since upon restarting the car the voltage normally sits at 4.95V exactly, but the longer it runs the more unstable it gets. Last time it dropped randomly and then locked in at about 3.5V and sank slowly, until I got bored of watching it at about 1.5V. Attached is a photo of the Nanocom readout, in case that's useful.

We've done the soapy water thing and couldn't find any leaks, and given the voltage is so dodgy on that left sensor I'd say that's the issue.

I'd appreciate any suggestions. What would be the next step to diagnosing the root cause? I'm not sure where the ECU is reading that voltage from so I'm not sure what to look at.

Hi ,

Have you tried swapping the sensors over LH to RH, to see if that makes a difference?
Oh, and there is no photo.


Cheers

As @neilly suggests, swap the ride height sensors over to see if the fault moves. If it does then you've got the culprit. If the fault doesn't move then it's into the plugs and wiring.
The ride height sensors are identical, the only difference is that one faces forwards and the other backwards.
Disconnect the battery before you disconnect the sensors otherwise you'll need to calibrate the suspension again.
At about $40 AU each, the ride height sensors are probably the cheapest components in the SLS system.

brian47 said:

The ride height sensors are identical, the only difference is that one faces forwards and the other backwards.

Click to expand...

Have you checked yours? both mine face with the "elbow" facing towards the front of the car.

Cheers

When the car is on even level set the suspension for coils with nanocom and if there is no leak it stays on level for days meanwhile you should find a known good SLABS ECU to rule that out

neilly said:

Hi ,

Have you tried swapping the sensors over LH to RH, to see if that makes a difference?
Oh, and there is no photo.


Cheers

Click to expand...

Oh I'm an idiot, photo added to first post.

I haven't tried swapping the sensors, that's a good idea.

brian47 said:

Disconnect the battery before you disconnect the sensors otherwise you'll need to calibrate the suspension again.

Click to expand...

Too late, I already disconnected the left one with everything plugged in How involved is the recalibration? Looks like the Nanocom can do it.

brian47 said:

At about $40 AU each, the ride height sensors are probably the cheapest components in the SLS system.

Click to expand...

Really?? I was under the impression they were very expensive, like $200 or so. Don't know where I got that info. Certainly excellent news if they're only about $40! I'll definitely look into swapping them left-right. At the very least, even if I can't attach them to the car I can see if the dodgy voltage swaps to the other side (fingers crossed that it does).

sierrafery said:

When the car is on even level set the suspension for coils with nanocom and if there is no leak it stays on level for days meanwhile you should find a known good SLABS ECU to rule that out

Click to expand...

Yep that's a good idea, that'd rule out leaks pretty nicely. No idea where we'd find a known-good SLABS ECU though. We'll try everything else first.

Thanks for the suggestions!

Hi ,

FYI, although it is not set in stone, I find that the reading for the nanocom should read in the region of approx 148 for the sensors when they are at std ride height.
When I have had to recalibrate the height using nanocom ( it is very easy to do) , I normally measure between the ctr of wheel and the wheel arch , std measurement is iirc 473mm +- 15mm . ( it is in rave)
I try to get both sides equal. I find that the two readouts for for the sensors on the nanocom do not read the same but are close.

But be careful if you are using the nanocom to raise the height it can very easily overinflate the height if you do not pay attention!!!

Cheers

As long as the problem is with the supply i doubt that the sensor has anything to do with it cos nanocom reads the ECU output for that, nanocom is not connected to the sensor's plug and the supply should be constant and equal for both sensors all the time , only the sensor's output(input into the ECU) is variable
here if form nanocom guide

· Left sensor supply: This shows the voltage of the left rear height sensor supply.
Expected values are 4.7 to 5.6 Volts.
· Right sensor supply: This shows the voltage of the right rear height sensor supply.
Expected values are 4.7 to 5.6 Volts.

neilly said:

Hi ,

FYI, although it is not set in stone, I find that the reading for the nanocom should read in the region of approx 148 for the sensors when they are at std ride height.
When I have had to recalibrate the height using nanocom ( it is very easy to do) , I normally measure between the ctr of wheel and the wheel arch , std measurement is iirc 473mm +- 15mm . ( it is in rave)
I try to get both sides equal. I find that the two readouts for for the sensors on the nanocom do not read the same but are close.

But be careful if you are using the nanocom to raise the height it can very easily overinflate the height if you do not pay attention!!!

Cheers

Click to expand...

Makes sense, thanks for the tips

sierrafery said:

As long as the problem is with the supply i doubt that the sensor has anything to do with it cos nanocom reads the ECU output for that, nanocom is not connected to the sensor's plug and the supply should be constant and equal for both sensors all the time , only the sensor's output(input into the ECU) is variable
here if form nanocom guide

· Left sensor supply: This shows the voltage of the left rear height sensor supply.
Expected values are 4.7 to 5.6 Volts.
· Right sensor supply: This shows the voltage of the right rear height sensor supply.
Expected values are 4.7 to 5.6 Volts.

Click to expand...

That's what I thought, but I don't know how the ECU is actually measuring the voltage... meh I guess I didn't think it through. That definitely sucks if it's the SLABS ECU causing the issue.

And yeah I know the voltage should be constant and equal. I guess I'm thinking maybe if something is shorting in the sensor it could affect the ECU's reading of the voltage. Again, depends how it reads it.

nanocom reads te ECU's output... yes, that shorting thing can be an explanation cos a short to earth on the wiring would make the voltage drop

The calibration will be needed anyway so to rule out a short in the sensor let nanocom plugged reading those voltages and unplug the sensor...if the voltage will still be low this way the sensor is ruled out though if it was a short in the wiring you should have got the SLS fault warning with a good ECU.... put axle stands under the body or at least one under the tow bar if you are "playing" this way