I got this info from "dmenheere" on another forum and just wanted to add it here for archival purposes with a few changes specific to already lowered cars. I also want to offer my sincere thanks to him for finding this info and forwarding it to me, as well as to the originator Kurt Lehman from the bmwe34m5 yahoo group. I owe you a cold one buddy!
Note: The wiring colors were a little off on the Touring, but the pin positions are the same. My changes/additions are italicized and colored for legibility.
Originally Posted by Kurt Leman
Originally Posted by Kurt Lehman on the bmwe34m5 yahoo group
"RE: [M5] Help ... "Suspn Leveling" warning ...
Let me de-mystify the SLS sensor for you. Despite all the info to the contrary, it's just a switch. In typical German fashion, a fancy switch with non-contact sensing (so it has an easy-to-define "on" band, and won't wear out under constant high-frequency suspension motions), but it's still just a switch output (technically an open-collector transistor switch output.)
The operation is very simple: Centered, the output is grounded. Too high or
too low (spec'd as suspension height +/- 10mm) and the output is open, pulled "high" (near 12V) by the instrument cluster input. You can easily check this circuit and sensor operation as follows:
1. The sensor passes through a 21-pin connector next to the battery under the rear seat. This is an easy place to probe. Looking at the back of the
connector where the wires coming out of the rear floor enter the connector, the 3 wires in the center row of pins on one end are the sensor wires, pins 12, 13, and 14. Pin 12 (three from the end of the middle row) is a black wire with brown stripe and yellow dashes -- this is the sensor output. The next pin (13) is the ground, and the end wire in the middle row (14) is +12V power. You can easily probe with a DVM in the back of the connector.
2. Turn the key to the first "on" position. You should see 11-12V on pin 12
with respect to ground, and 0V on pin 14.
3. Turn key one more click to the "run" position.
STOCK: With car at nominal height, you should now see ~0V on pin 12 (~.35V) and +12V on pin 14.
LOWERED: If your car is lowered you will see voltage on pin 12 still. -A/E
4. STOCK: Jack up the right rear of the car, and at some large height, the output on pin 12 will rise suddenly to near 12V again.
LOWERED: Jack up the differential carefully by an inch or two to simulate "stock" ride height, you will notice that the voltage on 12 has now dropped to ~0V. -A/E
5. STOCK: Lowering the jack should bring pin 12 back "low". If you load the car enough, you can trip the sensor to "high" state again. You can also undo the one 10mm bolt holding the sensor on (leave linkage attached) and turn the sensor to see the above readings.
LOWERED: Lowering the jack will cause pin 12 to go back high again. -A/E
6. Cars with no SLS simply ground pin 12 to defeat the warning. You can do the same thing if you want to ignore the message if your sensor is bad and you don't want to replace it, or if your car is lowered with an SLS delete kit. You can simply place a jumper wire between the wires leading to pins 12 and 13.-A/E