To fellow Guru Forumisters in the know

Would it be possible to install a switch in the cabin that could be activated just as it can be done with Audis, Mercs and BMWs, to manually lift the car so it can go slowly over larger humps to prevent under car scraping?

The engine management system can always override the switch when the car picks up speed or the lift is switched off.

I would love to install such a switch to fully pump up the compressor to help with those odd moments of avoiding scraping the underneath of the car.

 

Yes its possible

Each wheel has a height sensor. This is a just a variable resistor or more correctly a potentiometer(pot for short).
This is just like a volume knob but in our case the shaft is connected to the wheel

So as the wheel goes up and down the shaft turns and alters the resistance on the center pin.

All 3 pins are connected to the air suspension module. The two outer pins connect to power and ground and the third is the output. This creates a basic voltage divider circuit with effect that the voltage changes changes on the 3rd pin relative to the wheel height

So all you need to do is change this voltage

Getting back to your question here is how you do it

Here you need to cut the wire going from the sensor to the air suspension module.
These wire to a 4PDT switch to control 4 wheels or a DPDT for 2 wheels
One side of the switch goes to each sensor and the other to the air suspension module.
So when the switch is off you have reconnected the cut you made
The last connection of the switch goes to a pot.
This is wired up the same as the height sensor
The tow ends connect to the air suspension module (getting ground and power)
The 3rd pin goes back to the switch

Select a pot that is the same value as the wheel height sensor
My sensor value is 10K but yours may be different so measure it with a multimeter

All this is doing is emulating the wheel height sensor
You only need one pot for the all 4 wheels but could also use 2 or 4 if you need more adjustment

To dial in the pot first have the switch in the "normal" position
Read the voltage (supply is 5 volts) from one of the sensors and adjust the pot to match
This will mean the height does not change when you change the switch
Change the switch over to manual and slowly adjust the shaft
The suspension will no go up and down as you turn the pot
Once you are happy put some sealant on the shaft to stop it moving and your done

Cheers
34by151

 

Wow 34by151! You are a guru indeed.

Thanks for the advisory post. Definitely worth pursuing.

 

Glad to help. Post again if you need more help

PS I did a similar trick for the heated seats to make them hotter. In this case I added a resistor in parallel to the sensor. This just fools the ECU by making the voltage lower causing the heating pad to stay on and therefor get hotter

Cheers
34by151

 

+1 thx to 34by151.
I thought that was not possible with the sophisticated electronic command/control of the air suspension.
Though it still seems to me (not an expert) a delicate operation, not to make any mistake in the connections or balancing of the impedances.
May I ask you if you would have a simple wiring diagram available?
Also where and how do you make the pass-through to have the switch in the cabin?
Cheers,
Serge

 

Simply each height sensor is just a 10K pot
The rod attached to the sensor just moves the pot

Its all on fig 05.3 in the electrical manual

the easiest place to tap the wires is behind the rear seat at the air suspension module
All you are doing is switching out the center pin from the 4 sensors and inserting you own signal

here are the pots you need 10Kohm Spectrol 25 Turn Trimpot - Jaycar Electronics

Use a 4pdt relay on the 4 center pins to swich between the 4 post and the 4 sensors like this one 12V 4PDT Relay - Jaycar Electronics

Use a second 4pdt relay on earth the power or ground for the sensors

Run a wire under the wire carpet and up the console to the dash for a switch
he switch goes to positive and the new wire which in turn goes to the relay coil of both relays and then to ground.

So when the relay's are off you have the sensors and no connection to the pots
When the relay's are on you have the pots and not the sensors

So to recap the sensor is just a 10k pot
If you switch in a 10k pot you can set the height anywhere you want

The only caviat is if you set it too low or too high and keep it that way you can trigger an air suspension waring for reasons that should be obvious

If you want to test this just unplug one of you sensors
Measure the Resistance of the outer pins
Purchase a pot the same or near value
Connect it up in place of the sensor and have a ply with the wheel height

5 buck experiment to get you started

While i think of it if you do run a wire dont run just one 1
I ran a pair of 12 core cables (and 2 * 3 core video cables)
I only need a few of the wires in the first 12 core at the time but I think nowadays of the 24 wires I have about 8 unused

Before you ask the 4 video cables are used for the touch screen (RGBS) signal and the remaining 2 are used for the side cameras mounted in the mirrors. The come on with the turn signal do I get a 170 deg view of the turn on my screen

If you do a search you can find that install thread which shows running the cables

Cheers
34by151