Gents have been looking through the workshop manual to find out which sensor and where it is situated gives the information to the ecu that the car is grounded and so sends it to extended mode and can't find anything anyone any ideas\
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From memory think on the p38 there was a sensor on the front wishbone??

From memory: if all wheels (tires) loose traction. The suspension then goes into extended mode. If it still does not get traction it will go into extra extended mode after that. After that get out with a spade and some logs!!

Yes think you are right from what I have read which doesn't help me afraid but still good to know

Super extended mode is activated by the driver whilst in extended mode by holding the brake pedal pressed then pressing the raise switch.

Yes thanks it is just that mine goes into extended when I push for it to go into access mode

Hi Sandyt, mine used to do that as well and regularly give me suspension fault messages. I am currently under test to cure it which so far is going well.

I found out that the little brass muffler was blocked on the air compressor so I have removed it and currently have it soaking in some white sprit to try and break down whatever is blocking it.

As it happens this wasn't 100% the cure, so I further took off the desiccant canister (with the silica gel beads and filter pads in) used for drying the air in the system and found out that over half of the silica beads had turned to powder.

So while its hot over here for summer I am running it with no exhaust muffler and an empty desiccant canister and so far the fault has not re-occurred.

So I have washed the filter gauzes, will purchase some new silica beads and if my white sprit clean on the muffler doesn't work order a new one and hopefully that will all be sorted.

As for your original question on how the car knows its grounded, from what I have read, I believe that the suspension ECU monitors the values from the sensors on the suspension arms and, in your case, when you press the button to lower the suspension, the ECU doesn't see the values decrease as expected and therefore assumes that the car is grounding on something and automatically puts it in extended mode to allow you to clear the obstruction.

I might be wrong and I'm sure someone will put me right before too long if that is the case.

I believe there is also a "knock" sensor, so if your underbody hits something the suspension reacts. .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

No knock sensor for the suspension which wouldn't be of any use on loose gravel roads anyway. The static height sensor signals when the vehicle is meant to be changing height is the indicator.

Having posted I then searched the wiring diagrams but couldn't find one

Must have been the P38A .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Well going to work through it tomorrow and see what I find but as my poor old bus is 10 yrs old and nearly 150k on the clock may just replace the back bags (fronts done a couple of years ago and a new pump AMK ) and replace all 4 height sensors
bit of preventative maintenance - and then see what happens