air suspension through a Minnesota or Dakota winter: Escalade, Range Rover and Q7 owners, what actually fails?

this is my whole username. 2016 Range Rover HSE, the L405, 112k miles now, bought at 60k. here is the list from my own receipts. compressor at 78k, 1,450 at an independent in Denver, the AMK unit. front air spring at 95k, 690 for the spring and about 300 to put it in. and the one that matters for your question: at minus 15 the dash would throw "suspension fault, normal height only" on cold mornings and clear itself by lunch. that turned out to be moisture in the system freezing at the valve block. the compressor has a dryer with desiccant in it, and when the desiccant is saturated, water gets pushed into the lines and freezes at the first valve it reaches. new dryer desiccant is a 40 dollar part and an hour, and the fault never came back.

your one corner sagging two inches overnight is not a cold thing, cold drops all four corners a little and evenly. one corner is a slow leak, at the spring, at the line fitting on that corner, or at the valve block letting that corner bleed back. it shows up in february because rubber shrinks and a leak that seals at 40 degrees opens at minus 20. have somebody soap the fitting and the bag on that corner before it gets cold.

what i tell people: do not leave it in access height in the driveway, keep the compressor intake clean, and treat the dryer as a maintenance item every 60k or so. the systems are fine, they just do not forgive neglect.

i cross shopped a 2020 Q7 Prestige with the adaptive air before landing on the GX, and the Audi guys in the cities told me the Q7 system is the same story as above with different part numbers: compressor somewhere past 80k, the rear air springs first because they carry the load, and a level sensor arm that corrodes and throws the height off. the Q7 owner i talked to had 1,100 in a compressor at 91k and nothing else in six winters. so it is not a reason to skip a Q7. it was a reason for me to buy the truck with steel springs because i park outside and i am cheap.

from the return lane. under 50k, air suspension faults on Escalades and Q7s are rare on the condition reports, a handful a year. Range Rovers show up with a suspension message a little more often but still not commonly at lease mileage. what i can tell you is what the light costs: a truck that comes through with "suspension fault" on the dash gets 1,500 to 2,500 knocked off the grade before anyone even looks at it, because the buyers assume a compressor. so if you ever sell or trade one of these, fix the light first. the repair is almost always cheaper than the hit.

the Lexus side for contrast. the GX has no air, it has KDSS, which is hydraulic and does not care about temperature. the LX 570 has AHC, also hydraulic, and the thing it hates is old fluid, not cold. i see LXs at 150k with the original pump. so if you want the big Lexus and park outside, that is a point in its favor.

on the physics of the sag, the Colorado post is right. a gas loses pressure when it gets cold, every corner drops a bit, the compressor tops them up on the first key cycle. one corner means one leak. soap it.