Any Jaguar XJ owners out there like to play with the JLR SDD scan tool and find out how the air suspension works? If you have the SDD software and something like a V139 JLR Mangoose SDD Pro cable you can do it. Below are the detail steps:
Remove the electric connectors, unscrew the air lines and undo the two bolts of the valve block to the frame. I let all the air escape from both suspension and reservoir so I had to fill/pressurize the complete system again. That gave me some interesting insights. Because I wanted to flush out any debris/water in the valve block I decided to refit the air lines back to the block one by one (or two). First I ran the compressor to vent the line to the block, fitted the line, then I expected the valve to the reservoir would open but it did not. First the two valve going to the rear suspension open en the car is lifted from the rear. When the car is raised enough these valves close and both the front ones open to lift the car at the front. The way of filling is also described in the workshop manual.
After (unexpectedly) leveling the car first before filling the reservoir I then expected the filling of the reservoir would then be the final step but the reservoir valve did not open at all!
At this point I connected the SDD cable and did some testing just to check if the valve was good and if it switches alright. An interesting observation I made when measuring the pressure with the SDD is that you see the pressure going up (apron 12-13 bar) when the compressor is running and going down again to a remaining pressure of approximately 1,6 bar. All this time the reservoir was not connected at all. So the pressure you measure through the SDD is the pressure in the valve block and not necessary the pressure that is in the reservoir.
The car was at riding height so I decided to connect the reservoir line and go for a drive. I had a gut feeling the different modes of the suspension (Sleep Mode, Preliminary Mode, Post Mode, Stance Mode, Drive Mode) might have something to do with the reservoir not filling. Decided to connect the SDD and log the data during a 10 minute interval from the start.
The chart below shows the values I logged with the SDD, pressure, compressor on/off, reservoir solenoid open/closed, exhaust solenoid open/closed and the 4 solenoids of the front and rear airbags. I omitted the rear ones from the Excel graphic because they did not switch at all during my testing. I have done similar tests before an until now only saw the front ones switch occasionally and the rear never. Maybe on full acceleration they do.
So the starting pressure of 1,6 is what is measured in the valve block. The pressure in the airbags will probably be higher at this point and the pressure in the reservoir is still zero. OBD365
The first 140 seconds nothing happens and then the compressor kicks in. Normally the compressor has a cooling down time but my theory is that if the total pressure in the system drops below 3 bar the compressor kicks in no matter what to keep the car at height. In this case it has to because there is almost no pressure in the reservoir, normally that pressure could be used to allow for cooling time.
At that point I must have either braked or more likely drove over a speed bump. You see the front airbag valve open and the pressure shoots up to almost 7,5 bar. The opening of the airbag valves is probably triggered by the hight sensors. Then a few things happen, the compressor stops and the exhaust valve opens probably to get rit of the high pressure. Again almost immediately the compressor kicks back in and the reservoir valve opens again and after the compressor stops again the exhaust valve opens again. This happens another time probably to even out the pressure fluctuations. At 181 seconds the normal cycle resumes, compressor starts, reservoir valve opens and now steadily the pressure runs up to 11,3 bar. What is very noticeable is that the measured pressure drops really quick once the compressor is off and the exhaust valve opens. But since this pressure is measured in the valve block it does not tell anything about the pressure in the airbags or reservoir at that moment.
At the end you see the same pressure peak as before, probably another speed bump again.
Schakelgedrag luchtvering = switch behavior air suspension
Druk = Pressure
Compressor = Yep
Reservoirsolenoid = Reservoir solenoid/valve
Uitlaatsolenoid = Exhaust solenoid/valve
Vering voor = Front airbag solenoids
In case anyone ask, my SDD is from this shop: http://www.obd365.com/wholesale/jlr-mangoose-pro-for-jaguar-and-land-rover.html.